I have an auto, we would be trading wheels and tires. The wheels have a -6 backspace so they should clear. He's running them now with stock UCAs and says he's fine. Think I would be able to stuff them in there for on road use only without the BMC for a couple weeks?Is your TT a manual or auto?
Even with the heavier and larger tires I have not noticed a power difference. BMC is no big deal but You may need spacers with the stock 16s to clear the upper control arm.