http://bugs.winehq.org/show_bug.cgi?id=30232
--- Comment #11 from thanoulas thanoulas@gmail.com 2012-04-03 07:52:24 CDT --- ATi X1600XT is not affected by the slowdown.
Does this help? http://homepage.mac.com/arekkusu/bugs/GLInfo.html Based on that, wine's detection for HD4850 looks right to me