I'm new to Step Up Transformers

Please don't take what I am about to say the wrong way.  Whether an SUT would be to your liking or not is a subjective decision.  It really depends on what distortions your tastes prefer.  Everything has distortion.  Tube phono stages have different and generally higher levels of distortion than is typical for similarly priced solid state units.  Then you add an SUT and two (inlet side and outlet side) interconnects, which adds just a bit more distortion and perhaps noise as well.  Against that the SUT adds greater signal, which can improve signal to noise ratio and of course every SUT has a certain audible signature (yes that is distortion but it can be and often is pleasing to the ear).  So you see the addition of an SUT is not as simple or straight forward as it might seem at first glance.  The only way you can answer your question is to try one and let your own tastes be your guide.  No one can properly advise you beyond what I have suggested here.  This is something you have to do for yourself.  BTW, FWIW, in one of my systems I use a recently acquired Conrad Johnson ART Phono (their latest and greatest tube unit) with most often a Conolidated Silver Wire SUT although the C-J has enough gain to not need an SUT, so depending on cartridge and mood I often opt to forego the SUT.  I also have a Bob's Devices SUT which has a warmer sound and that is used too.  In my other system the phono stage is a PS Audio Stellar all solid state and it is used stand alone.  There is no right or wrong in this matter, no one size fits all circumstances, and in spite strong opinions strongly expressed in this forum and others like it, there is no one best solution.

Great info and advice!  Thanks so much.  

  My vinyl setup is a VPI Scoutmaster II table with a Soundsmith Paua MkII cart. 

I had a MM cart before so this is the first time I've used the Low Gain MC circuit in my Zestos. 

@rmcfee

I am quite familiar with both the Zesto and the Paua.

The Paua needs to see a load of at least 470ohms.

I fiound with my sample the optimum load at 1000 ohms.

I would strongly suggest you try on the moving coil input on the Zesto both the high and low MC input settings and both the 400 ohm and 1000ohm settings to find the best combination.

If you try an external SUT you must ensure that the SUT has a maximum turns ratio of 1:10 to be sure the Paua is loaded at a minimum of 470 ohms.

The Herron phono stage, now out of production but possibly available pre-owned, is another that achieves high gain with an FET based input stage followed by an all tube circuit. It was very highly regarded, one might say venerated, by some who frequent this site, before Herron closed down.