You'll need that extra 1GB of VRAM on the 7950 or 7970. A 2GB 660Ti or a 7870 LE will crash and burn when it comes to triple monitors. Dual monitors should be fine, as you'll more than likely only be playing on one.
If you do only go for 1-2 monitors, go for the 7870 XT/LE over the 660 ti. Currently, I can find the 7870 XT on amazon for £200, wheras the 660ti is £230 or more. Rather insulting, consdering that the 7870XT is stronger than the 660ti, doesn't have a memory bandwidth bottlenck and O/C's better. Get it together, Nvidia.