I'd stick with a 7.5" width. If you up the width of the tire, I probably wouldn't do more than a 235 or you may start rubbing.
Offset with a 7.5 should be in the 35 mm to 45 mm range for maximum bearing life, assuming the stock 7.0 is at 35 mm (a 42 would be best for 7.5 IMO)