Wheels-Tires "Safest" upgrade from 16in. rims

I have 18x9 wheels on my GT...255/40 frt and 275/40 rear tires. The fronts rub a little when the wheel is put to lock in a parking lot...no other issues. Stock springs. The rear tires are 3.9% taller than stock, so the speedometer reads that much slow...factor that for whatever tires you choose.

Your V6 appears to have the same air box as my GT...save your money on the CAI. I increased the size of the air intake opening of the stock air box by 3-4 times in the following manner:
--mark the rubber air snorkel/silencer at the place where it goes thru the fender well. Pull the air box from the car. Mark the rubber snorkel again towards the open end 3/4-1" from your first mark...this is where you cut the rubber snorkel in order for it to still stick into the fenderwell, but with a significantly larger opening. Seat of the pants suggests it works as well as the aftermarket CAI I took off, sounds as good, and best of all for you (in CA) it looks completely stock.