So, recently I did a massive update to my gaming PC - went from a Core2Duo to an i7 920, tons more RAM and an OS that can use it, and a graphics card that is about 2 generations better than my old one.

I saw a nice performance increase while 5-boxing, but nothing that was really AMAZING - Dalaran still killed me if I loaded in there on just 2 characters at prime time, and 5 characters would drop me down to 3 FPS, disconnect at least one instance of WoW half the time, and it was just miserable to try to get anywhere.

Then, on another set of forums I frequent, I saw someone mention the following tweaks to the Config file:

SET timingMethod "2"
SET componentThread "3"
SET M2Faster "3"

that are known to boost performance - basically they take change the way the game assigns priorities to various tasks.

Further, I saw that, since I just copied my wow install from my old machine to my new system that it was still set to use only 2 cores, not the 4+4 virtual that you can do on the i7's.

The end result is that after tweaking my config files I've got everyone merrily running around Dalaran with their FPS at the cap. Insane!

Moral of the story: check your config files and see if you can tweak anything to boost your performance!