The widest tire I have seen on a 17x7 is a 245/40 - as for it fitting your car only way to find out is to try
I would go with a 235/40 it will be around 25-26" tall and a true 7.5-8" wide - I would roll the outer fender lip if you haven't already
EDIT - If you don't want staggered tires I would go with a 225/40-17 to keep costs down on buying uncommon tire sizes
