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.
If you are only concerned with adding a third monitor for general use than a gt430 will get the job done plus it uses almost not power at all when idle. You can set physx to run on the second card for a small boost in physx games and if you are into folding you can run another client for extra points. However don't be expecting to gain the use of stereoscopic 3D across those monitors. The only thing you need to keep in mind when choosing a gt430 is to avoid the low profile models and there are certain normal height models to avoid. All the low profile models are terrible when it comes to power and cooling, the full height models that have similar build quality to the low profile models have a lot of problems. The good models have two power vrm phases to drive the gpu and one phase for the memory. The Zotac models are stable.