you'd need a 5mm spacer in the front. i'm running a 19x10 et40 (basically the same strut clearance as a 9.5 et45) with a 275 35 tire and i don't think i have room for a 285.
why don't you want to run a 275? 285 would start to look bloated on a 9.5 anyway.
I have a 20x10 40et wheel that I plan on eventually putting a 285/35 up front.... hope it fits. I believe anything over 40et you will need a spacer. Someone can correct me if I'm wrong.