time for upgrade?

My performance in dalaran is absolutely horrible, so maybe it's time to upgrade, here's my current specs:

nforce 680i mobo (don't know exact brand/type)
4 GB RAM
E6700
8800 GTX

main is on a 27 " lcd TV (1366*768), clones are on a 22" screen(1680*1050 divided in 4 regions)
graphics are already turned down to a minimum for the clones and run at 5 fps
main is also turned down a bit (viewing distance, shadows, AA, ...)

in dalaran i get really bad fps, sometimes as low as 3-4. At times it's so bad that the main wow just crashes...

What should i upgrade to get good performance? 5 fps on slaves doesn't bother me at all, but i would really like to run the main with everything turned on, and maybe even on a 50" plasma (1920*1080).

What's the bottleneck in my pc? RAM usage is usually 80-90%, but cpu usage is close to 100% on both cores at times.

4gig of RAM for 5 clients is the first thing I would address.

The first question would be what is your budget?

I'd say drop in a quad core and some more ram and you're set.

And (assuming you don't already have one) grab a 64-bit operating system, so you can use more then 3.25 gb of ram.

i'm using windows 7 x64

haven't really thought about budget, as long as performance is good it doesn't really matter, ofcourse it has to be reasonable.

So, 8GB RAM, a quad core processor, and a decent SSD, and your Dalaran experience should be great :)