When is it time to consider adding a SUT?

Thank you for your insight. It is very valuable. My question was not so much about there being enough gain but would the addition of a SUT improve the end to end performance of my set-up and wrm57 indicates that it wont.

I'll report back when it arrives to comment on the end to end performance.   

So we now have many posts quoting the science and others quoting user experience indicating that a quality SUT and cables may in fact improve the end to end performance of a high quality and capable PS even if they have sufficient gain required for LOMCs.
I am still waiting for my cartridge to come in and I will listen carefully for any anomalies even though one might not know what is missing until you try a SUT in the chain.  

I now have my Benz lps installed and about 12 hours on the cartridge. Changing the impedance settings from 100 to 1000 provide noticeable  changes in tonal balance. I settled on 500 as at 1000 there was some noticeable ringing on certain vocal tracks. 

I don't know if there are dynamics missing as the entire presentation is miles ahead of my previous Shelter 501 Mk II.     Ill give it another dozen hours and assess again.