I ran the stock 235/50-18 BFG's on the GT500 wheels (9.5 in.) for quite a while (10,000+ mi. ) with no problems. Like you, I didn't want to replace the 5000 mile tires when I put the wheels on. In my estimation it didn't look weird or anything, either.
2013 GT Premium, Red Candy Metallic, Brembos, Auto, GT500 Axlebacks.
SOLD! 2008 GT Premium, Vapor Metallic, 5-speed stick w/MGW, Ford Racing M6066 Whipple S/C, 3.31 gear, GTA's. GT500 front end, spoiler, suspension and wheels. Sequentials and one touch. - can't wipe the smile off my face.