Having asked similar questions about the GFT5 Gearkit, some feedback from Transmission experts is they question the 500ftIbs of torque capability of a T5, I explained the make and GForce give a very approx idea on what they think this transmission might take given certain criteria!
I think a syncro version would be marvellous with a 0.90 fifth gear (when they make that), behind a very healthy 347 engine, but if was a potential bomb, I dont want to go Toploader as they are to restrictive with 4 gears, a Richmond would be strong enough, but general opinion is poor gear change. In UNZUD (NZ) a lot of guys run the super T10 trans for racing behind big horsepower 630+ mainly with a pump to circulate/cool
oil, if they dont budget for a specialised track box.
I guess the bottom line is with the users and obviously being a relatively new product, not much feedback yet!