Fernando,
If the G4 refers to 'Group 4' the wheel widths you quote are not GP4, they are for a narrow body. (Group 4's would be 13" and 10" width)
On 17x11 rears I have Michelin Pilot Sports 335/35-17 and on 17x9 fronts I have 245/40's.
A lot of people seem to like 315/35 for the rears both in handling and as there is far more brand choice, which equals fewer $$. Hell, you can get 4 Sumitomo HTR Z rated tires in 315/35 size for the price of 1 Michelin Pilot Sport in the 335/35 size!
I think 255/40 width is about as wide as you can go on the front without excessive scrubbing at full steering lock.
Look on somewhere like
www.tirerack.com at the tire sizes you are thinking of and in the 'specs' section they will quote which rim widths they fit, e.g. 335/35 is for 11-13" rims, 315/35 for 10-12".
Good luck,
Julian