I am currently deciding which Graphics card to get at 1280x1024 res
45+ FPS is a playable standard for me on full blown settings with 4x AA
i might get another 17inch monitor so i would like to be future proof
a 4870 or a 5770 would be suitable for your system, you power supply should be able to handle it, and the rest of your components are fine, but if you buy a 4870 make sure you try to get one of the sapphire non reference ones
Best bang for buck, in the USA would be the $100 HD 4850. It's a capable card and could meet those settings in most games.
But even the (quicker) 5770 and 4870 recommended above still would not max 1280x1024 + 4XAA in all games (Crysis, STALKER, Metro 2033, etc.), so +1 for stepping up to these if within budget. The HD 4890 is even better, but likely far too expensive. This may be too muh for your PSU though.
edit: are any of these cards within your budget where you live, or are you limited to 5670's and 9800GTs?