amd phenom x2 1055t @ 3.2ghz
8GB RAM
radeon 4890 1GB video card
intel x25-m SSD

I have 60FPS on my main client and background clients set to 20max fps

The only time I don't get this is in dalaran when it's busy, my main may drop to 25-30fps but doesn't cause any lag.

I've been toying with the idea of getting a newer video card but they really aren't worth it since I'm still maxing out my fps and I don't have any lag... why spend the money?

EDIT: I run my main window at ultra settings and my other windows at "low" with the "draw distance" @ max.

Make sure you put antialiasing at x1. anything higher will just destroy your video performance unless you've got a super gpu