What is the difference between McIntosh MC275

I am thinking of purchasing a McIntosh MC275 amp to power my Tannoy Turnberry GRs. I can get a pretty decent deal on a new MC275 VI but I can also save a few thousand by purchasing a used unit. Can anyone tell me the differences in the IV, V and VI versions of the MC275 and if there are are differences sonically between the units.
There is this thread:


And I feel like there was another on this exact topic very recently but couldn't find the thread. Do some searching though the info is here.
That's perfect. Thanks Jond - much appreciated.