When is it time to consider adding a SUT?

andrei, I have to disagree with your statement that adding a SUT is not equivalent to adding another component, although you do make a good point that phono stages with enough gain for a low output MC usually use an internal gain stage to boost the output of the MC, which in effect is ALSO an added component.  (However, many phono stages with hi gain achieve high gain by the choice of the gain device [tube or transistor] used in the input voltage amplifier.  MM phono stages also add gain of necessity.  So sometimes it's just a matter of designing the amplification stage to suit one class of cartridges or the other.)  SUTs are not flawless, and adding a SUT also requires adding an additional pair of Interconnects and at least a pair of connectors in the signal path.  You might say that a SUT adds a different kind of problem, as compared to using a high gain tube or transistor to boost the low voltage signal of an LOMC.  Anyway, we agree that the OP does not need a SUT. Nor does he need a new phono stage.

gtaphile, FWIW, I'm using an ARC Ref 2SE with a Lyra Skala cartridge (0.5mv) and while there is enough gain using the high gain setting, I am much happier since I've added an Ortofon Verto SUT.   With the SUT, the dynamics, detail and headroom are immense compared to the sound without the SUT.   Also, without the SUT in the system, I could never hear any difference by changing the load.  Now there are significant differences by varying the load.  Just my 2 cents.  

I agree with taxmandme, my phone stage is a Conrad Johnson TEA2MAX, which has 55 db of gain.  This is a very high quality tube phono stage.  Although it can handle a range of cartridges from 0.3 mV to 5.0 mV, for any of my low output MC cartridges it is much better to use my recently acquired Bob's Devices Sky 10, set for 5:1 step up.  Much better.  There is a sense of ease about it, greater dynamic range especially noticeable during the quieter passages of performance.  As others have pointed out adding an SUT requires compromise.  In addition to the SUT, a very good set of interconnects is essential, so this is not a trivial tweek.

Dear @taxmandme : """  Also, without the SUT in the system, I could never hear any difference by changing the load. """

That only confirm that LOMC cartridge are " non-sensitive " to impedance load changes and confirm that in this regards your AR design is a good one.
What happens when you introduce a SUT in your hybrid PS is that exist a reaction inside the PS circuit wi9th impedance/inductance and capacitance and this is a real problem and not desired for the cartridge can shows it at its best.

Good SUTs sounds good but has its own limitations on noise and distortion levels and of course limited frequency range with out deviations where a good bipolar full SS phono stage can outperform your today set up.

Regards and enjoy the MUSIC not DISTORTIONS,
R.

There is only one problem with your analysis: "the bipolar full SS phono stage" that sounds better than even a mid-level tube phono stage is unobtainium.  Nice try though.