Hakaslak,

I have a similar setup to you:

Core i7 920 running stock (for now)
Asus P6T Deluxe
6GB RAM
1 4870x2
2 60GB SSD Raid0
XP x64
Catalyst 8.11 x64
850W PSU

I average 60-90fps in Dalaran.

Have you ever configured Keyclone commands on your current wow client?

Check for a maxFPS setting in config.wtf, which resides in %wow path%\WTF\ . If this has been set low, it will probably be the source of your problem.