Best gfx card for increased fps?

[Vanquish]

So pj is the cause of weird hitreg (this isn't an aim problem, I focus my crosshair on my opponent's body and sometimes I hear hitsound and watch my enemy die, sometimes I hear nothing; or maybe less hitsound, and then I die because I've used up a packet of ammo that didn't hit, giving the enemy time to strike while I reload or switch to pistol).

I'm confused. Help a noob out. :3