It entirely depends on you man.Here´s what I´d do: I´d take a stock GSXR-750 with 149 crank hp(like 129 rear wheel right?).So the thing would make the same amount of power as the 929/954rr,previous R1 etc.But it would provide much more rideability becuase of the less 250 cc.Then I´d slap full Akrapovic exhaust/power commander/air-filter and the bike would have somewhere between 145-150 rear wheel horse power.Enough to keep up with the new liters.It actually should be faster(especially on the track where it would provide great cornering).But this is what I´d do.You should decide what´s best FOR YOU AND ONLY YOU.The r6 on the other hand wold provide great cornering..but less straight speed.Don´t forget that the R6 is Supersport and the gixxer750 is Superbike.In the end I think I should say something a guy told me:Big bikez are for people who can´t make smaller ones go fast.