APEX makes a concave 17X9.5 ET35 that is awesome. You only need a 5mm spacer on the front. -2 degree of camber on the front would clear a meaty 255 like a Michelin PSS.
Performance gains made by 18s over 17s are negligible and only matter for looks, if you're a very good driver, or you just want 18s; which is ok.
The pic is of the 17X9.5
They also make a 17X9 ET30 concave wheel that could use a 5-10mm spacer in back for looks. This is a good option if you want to run 245s and don't have the required camber in the front.