I have almost the same exact specs as you. Same processor / video card but i have 8GB of ram instead of 4GB. I run vista 64bit and was having the same issues as you. I run 2 monitors a 30inch and a 20 inch for the clones. The weird thing is a reboot or starting all of my wow sessions would bump be back to normal.

Being a computer nerd i started to monitor everything (CPU Usage, Disk usage, bandwitch ect....) all of which seemed to be fine. I then when to my addon's and kicked everything out but Jamba and MikScrolling battletext..... Everything went back to 60FPS on the primary and the clones were smooth.

Only thing i have noticed is if i Cntl+Esc to open another program like IE or Crome.. my FPS starts to suck even after i close them.. Something pisses Wow off and it wont run good FPS until a reboot or completely closing wow's + keyclone.

My resources dont change after i have opened the other apps it just runs poorly afterwards.

Another thing that i noticed it that after the PC falls asleep and comes back out of sleep mode my FPS sucks.

Anyone have good luck on Windows 7??? Now that its released I was thinking of testing it.

PS i run smooth in dalaran and all city's when its working good...