I never owned an Ultimate but I have done comparisons with a Sig Mk II and Mk III. Both models have been paired with a Shelter 501 Mk II (0.4mV) and a ZYX Airy 3 (0.48mV). Volume/gain was never an issue with these cartridges since I don't listen to music at concert volume levels. Noise was a non-issue and was dead quiet, even between songs and soft passages so tube choice is critical (I used Siemens E88CC).
I had the same thought or scenario as you and was thinking of a step-up device but decided to go for a pre-amp that accomodates LOMC's.
I highly recommend any CAT above the Sig Mk III. The phono stage is one of the best that I've ever heard. If you find that more gain is required, get yourself a BENT-MU Step-up device (another great performer).