2 Different Nvidia Graphic cards?

Hi,
just two questions :)

1. I run FSX on windows 7 64 on i7 930, 6gb ram, GTX 480.

I want to run 3 monitors on TH2GO on one output, and on the other output a overhead panel. so 4 monitors on 1 grapics card. Will this effect frame rates badly?

2. I want to run 2 more monitors 10" displaying Flight Displays (PFD, MFD etc), can i buy say a GTX 460 and would this work? And will this also affect frames badly?

All this considering I run a Leveld 767 with full ai at Heathrow at around 20FPS with full resolution.


Cheers
Philip