18" All around:
If you wait a few months there are a ton of new Vette reproduction wheels coming out for F-bodies. Check eBay that's where I got my my first set of ZR1's and the prices were good. I bought my Z06 wheels from TomZWheels a sponsor on LS1Tech because they were the cheapest & widest 18" wheel I could find.
Make sure you put the right low profile tires on an 18" wheel or else you'll keep that 4x4 look.