what factory rims will fit a 06 Grand Prix?

Hey I'm trying to figure out what rims will actually fit an 06 Grand Prix. I thought about buying some GXP rims but I don't like the 8" front and 7" in the rear so I would want to try to buy two sets of 8".  Will this actually fit or is there a reason why Pontiac put 7 on the rear?  

I've also heard of people putting Bonneville GXP rims on there cars. They have the same 115mm bolt pattern so I was wondering if these fit and look good without having them stick outside the body of the car?

Thanks