Howdy!
The S motor system has replacable brushes and I believe a little higher quality EPIC motor. The T motor does not have replacable brushes and is more of your basic motor.
Unfortunately, I have not had the experience with my SS and the S600 motor system that Guapoman did (original thread creator). His vidoes look nothing like my plane
Mine is just putt-putting along and his flies like a super sporster should. So I don't know why my S600 doesn't perform like his, but just something I'm passing along. I use a 10x6 prop and it seems to work well, I haven't tried the 9x8 which comes with the kit, but that may give me the speed my plane is lacking.
For the money the SS is a GREAT value. I'm only into electrics and this plane is high quality. HOWEVER, I could not use the stock ESC for my plane. My plane only drew about 24 amps at WOT, but my ESC kept shutting off *ALL* power, including the servos. I got a new one from Great planes and that new one didn't work either. It should have been able to handle at least 30amps, but could not even handle 25 without overheating. I picked up a Castle Creations Peagsus-35 ESC as a replacement and haven't had any problems since.
Good luck!
David