Funny you should start this thread, having recently upgraded from an older MK.2 to an Mk. 4 with TNT platter,SAMA,and defeated supension, I am still in the process of fully realizing the differences, I can say there is a HUGE difference! not that the MK.2 is a slouch, its just that the 4 gets soo much more music out of the grooves. I know it's been said before but here it goes again "Blacker backrounds" etc,,,most of it comes from the better bearing and the High mass platter, and motor that is separate from the plinth,It is a very musical affair.
To sum up what we've discussed-the differences are the 19 2,and 3 are the same with the exception of acrylic plinth upgraded springs, lower mass platters and captive motor assembly. Their ease of set up is the same just a much better executed isolated motor and higher mass platter.
hope this helps