I've been playing with compilation options to try and improve response times, I haven't compiled the results, which in hindsight I now realise I should have! (Never mind!) However, I have got the following results building with GCC 4.5.1: gcc -O3 Works fine gcc -march=barcelona Works fine gcc -O2 -march=barcelona -fgcse-after-reload -finline-functions -fipa_cp_clone -fpredictive-commoning -ftree-pre-partial-partial -ftree-vectorize -funswitch-loops Works fine gcc -O3 -march=barcelona explorer crashes out (three times?) rundll32 crashes out winecfg loads gcc -O3 -march=barcelona basically breaks something badly. I'm not sure if Wine should support -march or what the policy is, or if this is even a Wine bug, so I thought I would post it here for comment. I see GCC 4.5.2 is released and these (http://gcc.gnu.org/bugzilla/buglist.cgi?bug_status=RESOLVED&resolution=FIXED&target_milestone=4.5.2) are the fixes, but I don't know if any of them would resolve the problem. I guess I can build 4.5.2 and find out... I have individually built explorer, rundll32 and ntdll32 with -O3 -march=barcelona and Wine runs fine, so I'm not sure which part of Wine is actually dying.