Rewindlabs is right, if you're gonna go any higher than that or want some futureproofing then a Radeon HD 4830 or 4850 would be more suitable. I would suggest the 4770 but HIS hasn't produced one with an IceQ cooler yet
You are going to want to go with ATLEAST a 4850 since your resolution is so high....most likely it will require a power supply upgrade...
Or the GTS 250 is another option...it is equal to the 4850...
You may not want to change the psu but to get anything in there that will allow you to play at your default resolution with the settings not all on medium than the 4850 or gts 250 are your best bets...you will also want to overclock them to push that extra performance out of em
In that case the 4670 would probably be sufficient.
I don't think you would need anything stronger since you're not using it for gaming.
But you might actually want something weaker like a 4650 or 4550.