Best video card options for improved GTA4 framerate

[Tonxi]

I have an ASUS M3N78 pro motherboard with onboard Nvidia Ge Force 8300.
2x2gb 1066 ddr2 RAM. Phenom 9950 Quad Core CPU and a Case 500w psu
with 2x 12v rails (14A+13A) anda 6 pin pci connector. I currently get a pityfull
5 frames/sec playing GTA4. What is the best Graphics card to buy to utilise
what I already have?
What would be the best card and psu to buy if I went a step further?
Thank you.
Martyn

 

[flyin15sec]

500W PSU, that is only really pushing 324w on the 12v. You will be pushing it with a HD4850, a HD4830 should work fine. 9800GT on Nvidia side should work too.

EDIT - Just realized you're willing to spend on a new PSU too. What is your budget?

 

[Tonxi]

I would like to stay under $300(Aus)