The 5870 is far more powerful then the GT 335m.
And judging by the system requirements the GT 335m should be able to run Guild Wars 2 with pretty decent settings, and like maxed on the 5870.
Regarding your last post, you said that the i5 should be able to handle it. Were you implying that the processor is more for running background programs while playing games and such? Or does it take part in making the game(s) run smooth? Because I know that is what the GPU is for....(Correct)?