AMD and PhysX games?

Do AMD cards just get awful performance in PhysX games?

I've recently tried to play through Metro 2033 (not last light, the original one, from 2010)

Literally 25 FPS with everything maxed.

Meanwhile, AVP (2011) and Skyrim (also 2011) run perfectly, as well as Crysis 2 (2011 as well) all of these games' settings maxed out, or nearly (motion blur off due to it causing me migraines, turning down AA by 1 or so to get to 60 FPS due to me being a FPS nerd)

So what's the deal, do AMD cards not like PhsyX games or...?

Not generally. Being that you have an x2 GPU card, it could be the Xfire profile for that game. Either try a different driver of turn off xfire.

AMD GPUs do not support PhysX on their GPUs, since it's NVidia's tech. If PhysX works at all, it will be handled by your CPU, which may or may not lower your FPS. Try disabling PhysX altogether (if the game allows it) and see if it makes a difference.