I wouldn't go much bigger then 8", otherwise the tires are gonna stick our real far from you're fenders.
Here is a comparison with some 8" wide rims I got from an 79 F150 to my stock 96 F150 rims.
Wider rims with almost 2" more offset.
96 300ci M5OD 2wd Reg Cab Long Bed 3.31 LS Gears and 8-Track player
A question that sometimes drives me hazy: am I or are the others crazy?