The CAI and a chip to go along with it will probably give you around those numbers. The 05+ GTs seem to dyno around 270 at the wheels stock and around 290 with a CAI and tune. If you get the CAI, you'll most likely need a tune with it. Some manufacturer's claim that a tune isn't necessary with their CAIs, but the 05+ GTs are very finnicky as far as changes to air intake. I wouldn't risk buying a CAI with out a tune designed for it, due to the high chance of running lean.
I'd recommend you check out Bamachips.com
and look at their JLT Intake and X-Cal2 combo.