FPS issue when using dual monitors in Vista32

Hi Long time lurker here

Come across an odd problem I haven't been able to fix
I normally run 2 machines using keyclone recently replaced one and happened to have a copy of vista. Decided to install it for all the DX10 goodies in other games etc
When I run 3 wow instances on it Main screen in windowed mode maximised on monitor 1 with the other 2 instances sharing 50% of the second monitor the fps drops to around 8 fps on all 3 clients

when i reduce the window size of the main instance so it's about an inch from the border of the screen on all 4 sides the fps jumps back up to the 70fps it's capped at. It'll also run at the fps caps if i run all 5 wow instances on 1 machine one 1 monitor

Machine 1
Q9450
Nvidia GF9800GTX
4gig ram
and 4 drives with 4 separate copies of wow on each drive
Vista 32

the older XP machine which never had this problem
AMD 4600X2
2gig ram
Nvidia 7900GT
4 Drives Wow on each
WinXP


Any ideas what could be causing this ?


Thanks
Rob

One possible fix might be to turn off v-sync in WoW and re-enable it through the nVidia control panel. (I'm assuming you're using nVidia -- might work for ATI too.) That helped me quite a bit on Vista x64, but I still can't run on 3 monitors without unacceptable slowdowns :(

If you're getting FPS trouble when a window is hanging slightly over into the next monitor, that's purely a graphics bug. Back in the old days, not only could you not do this at all, you couldn't even run Direct3D surfaces on a secondary monitor. They eventually fixed that about a year after Win2k came out but the support is still very much reliant on the graphics drivers to support it well. You might be running into an issue with NVidia's Vista drivers there. Easy test is to swap the video card onto your old machine on XP and see if you get the same behavior. If not, then it's either Vista itself or the NVidia Vista drivers. If it happens on Xp as well, it's a general issue with the NVidia drivers.

Hope this helps.