Which ATI Graphics card for my system?

I am looking for a suitable video card, to me games like GTA IV, Race Driver Grid, etc. redundant, but not excessively high resolutions and details displayed. I have CRT, and also at 1024x768 or 1280x1024 still good enough. Have there one model from ATI thought, because in the 2D mode is not as loud as NVIDIA ....

My system:
Asus M2A-VM HDMI
AMD5200 X2 EE
520W PSU
4GB RAM 800
Heaps of disk space

The thing is really quiet until now (which should, where possible, at least in 2D mode to remain so) and HD material is smooth again, but with GTA4 for example, increases the graphics chip with the error message "nothing there, no pixel shader 3".

What fits best?
And where is the difference from 4670 to 3870? Not by sight, just go to the memory interface? Then 3870 would be better .... but is not "outdated"?

the Hd3870 is slightly faster than the Hd4670, I would in your place would purchase HD4830 because so that I can play GTAIV.

Ok, I will probably also, but bored with the card not in my system?

well your CPU is not the fastest but a HD4830 fits very well into your system and if you eventually upgrade your CPU you will get enough power by using this card .