The 04-06 GTOs have a 5x120 bolt pattern, which is shared with many BMWs models, and you'll see plenty of overlap in fitment. There's not a lot of room to run wide wheels front or back due to the strut clearance up front and wheelwell design in the back. If you run an 8.5" wheel up front, shoot for 40-45+ offset, and a 9.5" wheel out back will require 45-50+ offset. That will allow a 245 front tire and 275 rear tire. VMR wheels are very popular due to the reasonable cost and offsets available.
Or make it easy on yourself and find a set of factory 18s and call it a day. The look of those is hard to beat.
Last edited by MWR; 02-06-2014 at 10:50 AM.