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