They are 16" x 6.5" (I'm pretty sure) with a +45 offset.

17" x 7" will fit no worries, you could put 20's on if you wanted! The American market gets 17" x 7" standard.

Why not go 18's??? 17's are too small!!! 18's would look much better and you still have a 40 profile tyre, not rubber bands. They are not that much more expensive for a full set of mags and tyres.