I’ve had a MBP retina for a while and have to say that games run sweet on Windows via boot camp (GW2 no exception, looks fantastic and runs fantastic), sure it literally burns your fingers off during play but it’s ok for a short gaming session. Generally I’ve found Windows to be a faster and smoother than OS X (both Lion and M. Lion) both in desktop and gaming and don’t really see the merit of native OS X clients when Windows outperforms in every way in the games department. This is certainly the case for all the Blizzard games excluding World of Borecraft which I don’t play so haven’t tried.