Sounds to me like you should get good fps with your setup.
I'm running 4 windows on 1 PC with the following specs:

2.4 GHz Quad Core
4 GB RAM
Gefore 8600GT 512MB
Windows XP x64

Although my specs are a bit higher, I still think you should be able to get good performance just running 2 windows.

Also if you want to get rid of the borders you might wanna checkout WoW Maximizer or KeyClone's maximizer. (Don't know the links right now, but the info is in the stickies at the software forum)