I suggest you go for this: http://www.newegg.com/Product/Product.aspx?Item=N82E16814121272
$149.99 after mail-in-rebate !!!
preOC to 680/2100, this HD4850 can be clocked easy to 730+ which is much closer to 4870s. Plus you get brand new 4000 series of ATI!
This HD4850 is faster than 9800GT and 3870s especially when you OC. I suggest you to go for the newer chips rather than last year's techlology.
Look at the graphs that shows pure GPU-score on 3dMark vantage: http://www.hardwarecanucks.com/forum/hardware-canucks-reviews/9791-geforce-9800-gt-roundup-evga-asus-gigabyte-palit-11.html
This shows only GPU rating without mentioning the CPU.