The GTO is rated at 400 HP and 400 TQ so as you can expect it has more grunt. But it's hard to say which feels faster. In the GTO it's a fairly constant power curve so you get pulled back into the seat like you would expect, and I think it is significantly faster than the R, even with the tune, but with the constant power it doesn't really feel quite as urgent. The thing about the R is that it has power... and then the turbo kicks in, and it has a LOT MORE power, and immediately you feel it, so it almost feels MORE powerful than the GTO. But I know it isn't, it's just an illusion caused by that kick in the ass you get at 3,000 RPM.
In every other way, the R is better, as you would expect. Handles better, rides better, shifts better, quality is better... and so on.