You will need a power supply upgrade as well, I suggest an antech 550w; it is a great price right now on newegg and A 560ti will be a nice balance to your system as well as keep you happy for every game you play. Have fun and happy gaming. What is your budget as it will help determine our suggestions for you
Re the above link - those power draw figures will be with a less thirsty CPU than your C2Q 9550 - but don't forget to subtract about ~20% from those peak figures for actual PSU draw, since those figures were taken from the wall.
PSU will most likely be fine with a lower end GPU (6870 would be here an option IF and ONLY IF its a good brand PSU).
I dont think its any worth it getting a better gpu than a 6870 or a 560 Ti (new revision when it comes out) since i have 1900x1080p and so far a 1st version 560 Ti is enought for MOST games in max settings. Maybe not in like 2-3 games, but thats it.
Thanks for all the quick and useful comments!
Indeed, I had my eyes set on the 560ti but I was afraid I'm aiming too high.
Regarding the budget - It's not really an issue, as long as it's cheaper than buying a new pc.
I though about buying the best card I can benefit from given my other specs. If I need to spend a little extra for a new PSU, it's no problem at all.
If you do not want to install a new PSU, then you may be able to install a Radeon HD 6770 (re-branded HD 5770), but you need to provide the make and model of your PSU. Listing the available amps on the 12v rails and the total maximum watts on 12v rails will be useful too.