What would the diffrence be between a HD 6450, and a GT430.
I can't really find any good information on this stuff.
I really don't understand what you are trying to ask here. You have a GTX 480 and you want to add a second GPU for more monitors? I'm not very familiar with multi-GPU configurations but I would believe you would need a second GTX 480 and SLI them.
I wonder if you could set the 430 as a PhysX card and then have a monitor plugged in?
As much as I know about this subject, I would think it won't work. Your best bet would to sell the 480 and get a current gen 7950/7970 if you want multiple monitors.
Again, this is if I am understanding correctly what you are asking. As the 430 vs. 6450, I would say the 6450 is the better choice, but I'm probably wrong on that.