I am currently running 255/35/19 F 295/30/19 R AD08's and I can say I have some mixed opinions...
-the 255 fronts do offer A LOT more grip in the front, I can do things that I couldn't do with the stock 245's.
-the 295 rears are the perfect amount of grip in the back. The rear end just never looses grip.
-The Look AWESOME.. The sidewalls are dead squared and not stretched one bit. You will love the way the 295's look tucked under
-255 fronts rub at 3/4 turn on the back side of the inner liner
-255's loose the crispiness of turn in feel compared to the 245's
-295's rub on the rear part of the inner fender liner on hard dips
Heres what I recommend. If you need the front grip (you track, you auto-x, you go into the canyons EVERYDAY) then get 255/35/19 fronts. The only objective thing that I do not have a answer to is that maybe with a different tire up front you may not loose the crispiness of turn in feel with the 255's.
295's. YOU HAVE TO TRY THIS AT LEAST ONCE... The feel freaking AWESOME.
Personally, I think I will do 245/275 next time around. I'm sick of two things; One is the rubbing and two is the less crispy feel of the 255's. I personally don't like the look of the gts setup of 255/35/19 fronts and 285/30/19 rears so I strayed away from that.
My reason of upsizing was in two parts; The rears just didn't have enough grip. When I was going WOT on a incline on ramp on a fwy where the temps were around 55 degrees out, the rear would twich as if it were to loose patches of grip. Another reason why I didnt like the rears was because when i was in a turn and I would get on the throttle lightly, I felt like I was very limited to what I would be able to do with the car. The car was able to handle it, but I would feel the rear loosing patches of grip.
I had a 245/295 setup going into my first trackday at chuckwalla and this is where I could feel the extra grip in the rear. I got to appreciate this however the front 245 tire was SO limiting. Understeer was so easy to do with the 245's. So I upped to 255's and on the street they're amazing. I am convinced I do have a better setup but I don't want to make judgements until i get back on the track.