Choosing an SUT?

I'm shopping for an SUT, how do I choose one.  My cartridge is a Soundsmith Zephyr MIMC ES star lomc cartridge.

Compliance  10um/Mn
Voltage          0.4 mv

Any suggestions? 
Call Bob Sattin at Bob's Devices for a Cinemag 1131 with switchable gain. Do you currently run the MC input on the Chinook?
Search around, there is an absolutely incredible number of different SUTs  out there to choose from. I do an awful lot of due diligence before buying anything. Many hours have been spent reading literally hundreds of pages on this one subject alone. There's websites of guys devoted to SUT who have tried dozens of these things. If you can find the right one, or maybe even if you can't, a SUT may be the most magical essential component ever made and will open doors unimagined in your musical experience. Or then again maybe it will just be a source of hum and noise and endless frustration. Which is why you don't see one in my system. But may also be why you will fall in love. I loathe pointless cliche'd writing but if ever there was a time to close with YMMV, this is it.
I just was on the soundsmith site where Peter Lederman recommends a transformer with a 1:10 ratio and >470 ohms.
To answer the question about using the mc input on my Chinook the, answer is yes. I am doing as much research about them as I can.  I want to experiment to see if I can improve the sound. 
When I spoke to Peter Lederman about the SoundSmith cartridges his recommendation was a minimum loading of 470 ohms and preferably less (higher number). I subsequently acquired one of Bob Sattin’s Sky10 SUT that has a 1:10 ratio setting with 470 ohms or a 1:5 ratio setting with 1880 ohms.  I don’t currently have a SoundSmith cartridge but employ the SUT with a Kiseki Purple Heart that has an output of 0.48mV and performs well on either setting into my MM (44db 47k ohm) input.
+1 @chakster
i can understand it if you want to avoid the JFETS in MC input, that may give better sound but a gain of 60db should be more than enough. 
You bring up good points about the gain achieved by the Chinook.  Other owners of this phonostage have indicated the superiority of the mm side over the mc side.  With a transformer I can exploit this advantage.   It would be great to audition candidates to see if it's true. 
When using my Herron VTPH-2A, which is also a JFET MC gain stage, I greatly prefer the sound using a SUT into the MM tube section.  I've used several carts ranging from 0.3mV - 0.5mV this way and always prefer the SUT into the Herron.  Similar results with the Chinook wouldn't surprise me.
I have not found the low impedance MI carts to be a good match with SUT's.  While the reflected resistive load can be kept in line with what peter suggests, any capacitive load also quickly comes into play and causes a LC resonance with the cartridge inductance that quickly encroaches on the top end of the audio band.

the link below has a spice simulation of a 10Ω 2.75mHy MI cart into a 1:10 loaded with 47K.  The plots show 100pf, 200pf and 300pf of capacitive load.

I am considering trying an SUT for my SoundSmith MIMC Star into my Herron VTPH-2A. Sounds like arguments for and against this set up. Think this will work?
I am considering trying an SUT for my SoundSmith MIMC Star into my Herron VTPH-2A. Sounds like arguments for and against this set up. Think this will work?
I got a SUT from these guys:   They were recommended to me by someone with a lot of experience with SUT.  For a small additional charge, they will do a custom winding to match your cartridge if that is needed.  I am happy with mine but it the only one I have ever had in my system so can't compare it to anything else.  They speak English and were very easy to deal with.
I too found the Bob’s Devices Sky SUT preferable to the Herron’s JFET stage (though it is a very good JFET stage). As others mentioned, there are loads of SUT options, each with their own sonic profile. The Bob’s Devices are rich, robust, and fleshy sounding - on the warm side of things. They work well with a wide variety of cartridges.

HOWEVER, the thing about SUTs is that it can be tricky to balance optimal gain vs. optimal load if you’ve got one of those cartridges that asks for a relatively high ohm # for loading versus its output. This is somewhat the case with your Zephyr. Asking for more than 470 ohms load (others have mentioned it may benefit from a higher #) from a 0.4mV output is tough. You’re either going to be on the low side of optimal for gain or for ohms. Some folks are OK with less than 4 - 5 mV coming off of the MC step-up stage but I don’t like it.

One way to combat this is to find a phono stage that allows for flexible loading above 47K ohms in MM mode. Unfortunately this is more rare than it should be. I know the Rogue Ares allows for this (47K, 100K, or even 1 Mega-Ohm MM loading!) and so it can be a good partner with SUT for the usual "tough for SUT" crowd like the Benz non-magnetic ruby plate cartridges and (apparently) your SoundSmith. The Ares MM stage will be a slight step down from the Herron, but might be comparable to your Chinook. Then again swapping phono stage is a lot of effort just to try out a SUT!

One more consideration for SUT is that you will need a very short run of shielded low-capacitance RCA cables coming OUT of the SUT. If you want to hear cables make a huge difference IN A BAD WAY, then swap in some large gauge fire-hose braided geometry interconnects more than 1m long. Also you might have to deal with ground loop hum gremlins. The things we do for love (of analog)!
If you have a condition where you have too much gain with the VTPH-2A you can use 12AT7s in all 5 positions which will lower the gain by an additional 5dB. Always, make sure you are using long plate 12AT7s such as the ElectroHarmonix 12AT7EH in positions V2 and V4.  These have more grid to plate capacitance and will keep the passive RIAA network from sounding thin (no feedback is used in the VTPH-2A). For more gain use short plate 12AX7s in positions V2 and V4 in order to keep the RIAA response accurate. If you originally purchased a 4 x 12AX7 version  (we did not sell many of these)  the rules are a little different for V2 and V4 - those can be long plate 12AX7s. Check the back of the VTPH-2A for the tube set markings. When tube rolling you can use any 12AX7 you want in positions V1 and V3 on either version of the VTPH-2A. 12AU7s will not work in this design. Tube locations are marked on the circuit board and in the owner's manual. - Keith Herron
Thank you all for the thoughtful replies especially you @600ohms !

I’m looking at the Zesto Andros Allasso which has variable gain and load. Thoughts on that device?
I’m looking at the Zesto Andros Allasso which has variable gain and load. Thoughts on that device?
It is quite likely a nice SUT, but the Allasso has a LOT of loading options you'll probably never use with your SoundSmith. It gives you the option to load DOWN your cartridge, which (as per manufacturer recommendations of 470+ ohms) is the wrong direction for your SoundSmith. You'd probably end up using either 1:8 or 1:12 in the 10th loading slot, which is the same net result as any regular 1:8 or 1:12 SUT *without* those loading options. Now if you could plug it into an MM stage with its own loading options up to 1 Mega-ohm, then the Allasso would give you a rich array of loading selections appropriate for your SoundSmith - but of course you'd have to recalculate the loading slot table to see what they remap to for each gain ratio!

With your Herron, I'd wager that its JFET stage is still your best option for that particular cartridge. You can still experiment with different loading plugs, and tube roll to capture some of the extra "body" that a good SUT would typically impart. That's what I heard when I hooked up a Bob's Devices Sky to the Herron, though my cartridges had 5 ohm coils and liked the ~129 ohms net load!
Call Kevin @ K&K Audio, he'll build one at very reasonable cost for you.
This thread has had authoritative input from two solid professionals in the business, Intactaudio and 600ohms. Intactaudio actually posted real data! I would advise the OP to pay most attention to those two sources.