I'd recommend a 5750 or more for high detail in new games. The 5670 would handle some games at high, but it'll struggle with others, especially if you want full AA.
Also, it's worth mentioning your really going to start having a hard time with some new games and your current cpu. Your to the point where you've fallen below the recommended on a number of games, which usually isn't a good thing.
The HD 5670 is good enough to play most current games @ 1440 x 900 at pretty high, but not max graphics quality. The HD 5750 is not too much more than the HD 5670 and will allow you to max everything at your resolution.
The HD 5770 is not much more than the HD 5750 roughly $20 - $25 when there's a rebate or sale involved. It will last you a while and if you decide to upgrade to a higher resolution monitor, then you will not feel the immediate need to upgrade the video card.
4670 < 5670 < 4770 < 4850 = 5750 < 5770 < 4870 (just by a little bit)
Your CPU will hold you back sooner rather than later. Probably good enough for the HD 5670, but it will hold back performance of the HD 5750 slightly and the HD 5770 a little bit more. You will differently see increased FPS as you go up the chain; I'm just saying you will not see the full potential of the HD 5750 and HD 5770.
thank u guys for ur inputs... well i wanted to get a new cpu and mobo.. the i5 750... but then i'm student who has to get all his money still from his father... and my father's in a bit of financial crunch... from the money i've saved up i can only afford a $100-$120 graphics card.. for the cpu i have to wait some more months...
so i decided i'll buy this 5670 for now and later upgrade to a sandy bridge cpu and more powerful card later along with it... may be an year from now when i'll be earning...