g'day, I noticed no one had posted so i thought id let u know my setup.
I have 8" wide on front and 9" on back. offset for both is +32.
I think you could definetly go half an inch wider on back, but im unsure about front. My next set of wheels im ordering soon are 8 on front and 9.5 on rear, i am unsure of the offsets however.
A guy i know with a stock R33 gts-t claims he has 10 inch wide rims on the back, I guess its possible but im unsure.