I've got 275's on the rear & 245's on the front w/ 8" rims. 275 is pushing it a bit out back, but I like the way it looks and it hasn't caused issues. If you've got 10"s out back like said above go around 295
8 inches wide.
275's on a 8 inch will work, but it will look like a bit of a stech IMO.
255/45's are a good all around choice for 17 x 8's. They are a bit bigger than stock (245), then won't rub, even when lowered, and you can still rotate 'em.