17x9.5 +15 all around. 215/45-17 upfront and 235 or 245/40-17s in the rear. Done an done...
The difference between the G35 wheels and the 17x9 +30 is that the extra inch. Basically, you end up with half an inch on the inside of the wheels (towards the strut) and half an inch to the outside towards the fenders. The problem you will have clearing will be the inside part. Depending on the suspension, you will more than likely need a 5mm spacer to clear the inside.
If you need a reference on what 17x9.5 +15 would look like...heres a set of my old wheels. 18x9.5 +12 with 235/40-18s all around
