Video card recommendations

I just had a Monitor die and this is the first time I have run my mac pro with only a single monitor. It has the low end GT 120, it is much more responsive and faster at moving images from LR to photoshop with out the second monitor hooked to it. I need to go back to 2 monitors! When I do I would like to keep this level of performance that I have with only one monitor. Should I buy another 120 and run each off its own card or buy a better card and still run each off of its own card. I will also be adding a HDMI card for final cut work hooked to a LCD TV as a 3rd display.

Any suggestions will be most helpful
Thanks
Bob