Please help me choose GPU.

Hi
I want buy new GPU...
Now i have 8600gts
In GTA 4 average fps is 30-35 on low settings...
My system is
CPU C2D e6600 @ 3,2ghz (400 x 8)
Ram 1x2gb G.Skill 800mhz @ CL4-3-3-9
And im finding better video card for GTA IV...
I Think buy HD4830 is this card (And my CPU and ram) enough for GTA IV?
I will play on 1680 x 1050 res.
I can't choose between hd 4830 and hd 4850 cards.
In my country 4830 coast 145$, but 4850 210$... Is this price worth performance?
Or maybe take 9800GT? (Coast 165$)
What u think, guys?


Thanks!

Sorry about my English

Nice overclock on the E6600, I`m still using stock!
GTA IV is very demanding, even powerful quad-core systems struggle with it.
I`d say the HD4850 is the best choice.
What country are you in? I`m stuck in cold, wet, England.