Video Card... Is more Vram or stronger GPU better?

When multi-boxing 5+ WoW clients, is it better for the Video Card to have more Vram or a stronger GPU?

currently the two cards I am looking at are:

- AMD Radeon HD 6870 - 1GB;

- NVIDIA GeForce GTX 460 - 2GB;

Since I am using ISBoxer on one monitor with multiple WoW running, I am not sure if the video card's GPU or Vram is more important.

I believe the HD6870 is a stronger GPU but the GTX460 has double the Vram (2GB vs 1GB).


Anyone have any thoughts or recommendations?