if it's a desktop, i recommend getting a mid end nvidia graphics card, then overclocking it using ntune, remembering to apply advanced gpu cooling. better fans, bigger fans, liquid cooling system if you have the dough. :p (if so, i recommend using beer instead of water)
this way, you don't have to spend too much extra money on a better graphics card.
however, you may have to consider that high end cards offer more vram. your call.