Only Metro 2033 out of these 4 games makes a use of graphics card accelerated PhysX. I found PhysX effects not worth a while but you may like them more than I do.
Give it a try, it shouldn't have any negative impacts on your system although I encountered three problems when using PhysX card with ATI:
1) both cards were running quite hot which wasn't making me happy in any way
2) XFX GeForce 9600GSO is a one slot cooler version, what made it 'a bit' louder than mine 5850 is
3) I don't know if it is an already resolved issue but I had to make a virtually extended desktop to run PhysX card properly (even though I was using modded drivers for PhysX). It got slightly annoying that your mouse cursor doesn't stop at the edge of the screen
- yes, as for PhysX that is
If you're a PhysX freak and have crap loads of money, go for watercooled 480GTX SLI setup, do some benching and brag on Youtube about their performance in Metro 2033. £1000 worth of graphics cards should do well in any game out there. You could always cut the cost in half and get a 5970 but who the **** cares...