40 HP is alot. It's the difference between a lower-model Civic and a GP GT, or a V6 Mustang and the V8 Mustang (older models ..). Not to mention the GTP has ~60 more ft/lbs torque, which is what you should really be judging off of.

Other than that, I agree with the previous posts. It depends on what you want out of the car and how you drive and how much you drive, how much you want to spend, etc. But there are no differences that result in more problems with GTPs than GTs.