17x8?
I'd say a 255.
A 265 would have too much bulge, and just not look right at all (unless Nitto, they tend to run more narrow than others)
265/275 is the perfect width for a 9" wheel. Yes you can fit wider of course, but it won't look right. I used to run 295/35s on my rear 18x9 Saleens many years ago. Lots of sidewall bulge.
Anything bigger than a 255 on an 8" wheel would look similar, and be potentially dangerous as well.
So to sum it up, you can put a 265 or 275 on an 8" wheel, but in no way would I recommend it.
255 would be my "final answer".