http://bugs.winehq.org/show_bug.cgi?id=12453
--- Comment #74 from Henri Verbeet hverbeet@gmail.com 2010-07-21 07:38:39 --- Created an attachment (id=29733) --> (http://bugs.winehq.org/attachment.cgi?id=29733) patch
Please give the attached patch a try. It's of course not going to be as fast as disabling sRGB completely, but it should reduce the cost of RGB <-> sRGB transfers a bit.