Oh I must've misread. I swear it said 255? Ohwell, my mistake.
I would stick with 225/40 on there. 235 is a bit big, and I dont like it. But Gary likes to get as much rubber as he can on the rim, he puts 245s on 8s.
I've got some 17x9 +20 that I've put all round on my car before, they stick out ~20mm, so you need to do a fair bit of guard rolling. It looks damn tough with the offset though, clears all the suspension easily. I had 215s on them at the time though, so I'm not too sure how 255 would go, but I was looking at the edge of the rims. I can send you some pics of how they stick out if you want?