WoW Framerate Problems

Hi guys,

So I have a decent build, and it runs Crysis and Crysis Warhead pretty decently, so I was very puzzled when some areas in WoW gave me major framerate issues. Here's my specs:

AMD Athlon 64x2 5000+ BE at 3.0gHz
2 2x1 GB PC26400 Ram for 4 GB total
ASUS M2N SLI Deluxe Mobo
2x 8800gt 512 MB in sli
Antec 1200 Case (good cooling)

In areas like Shattrath City, my framerate drops as low as 5 sometimes, which just shouldn't be happening. Has anyone come across this issue and found ways to fix it? I've checked the Blizzard forums and some people say it's just shoddy coding, but the problem seems to pop up for some and not for others. For instance, my laptop, which is clearly inferior to my desktop, runs it perfectly fine.

Does the fact that I have 4 1 Gig sticks of memory have anything to do with it? Like trouble accessing memory fast enough?
If I plan on getting like a cheap instaboost of an upgrade before actually building a new rig in the future, would getting 8 gigs of memory make a big difference? (not just for this game but in general)

This last question is a little unrelated, but if I wanted to change vid cards, since the SLI is a serious headache, would a 4890 perform better or worse?