I have the same size wheels on my Roush and they came with BFG 295/35/18s in the rear and 265/35/18s in the front. They were great tires, however I now have Toyo Falcan's, but with 285s in the rear. A good choice too, at a much better price. Go with BFGs, 295s in the rear if money is not an issue, Falcan 285s if it is. I wouldnt go any smaller than a 285 on those 18X10s. Stay 265 up front.
I have the 265/35 front and 295/35 rears on my Roush also. The BFG's are $$$$, but I plan on replacing the rears with Nitto 305/35's when the time comes.....
BTW, pics in my sig if you're wondering how they'll look.
As long as you go up in rim size you can go down in sidewall size with no worries about the speedo being messed up. For example.
17's=45 or 40
18's=35 or 30
BTW I have 265's front and 285's rear. Wish I would have went 275s in front. 285s are okay but still should've went 305s
Jon