IMO, best thing you can do is rip that 8500 off your PC, grab a sledgehammer and give it a good whack.
After that's done, go to newegg.com and order any of these depending on your budget (and your PSU, you should crack your case open and check it).
(No PSU change needed)
POWERCOLOR AX4670 512MD3-P Radeon HD 4670 512MB 128-bit GDDR3 PCI Express 2.0 x16 HDCP Ready CrossFire Supported Video Card - Retail
http://www.newegg.com/Product/Product.aspx?Item=N82E16814131122
(Possible PSU change needed)
SAPPHIRE 100265L Radeon HD 4830 512MB 256-bit GDDR3 PCI Express 2.0 x16 HDCP Ready CrossFire Supported Video Card - Retail
http://www.newegg.com/Product/Product.aspx?Item=N82E16814102803
(Possible PSU change needed)
SAPPHIRE 100245L Radeon HD 4850 512MB 256-bit GDDR3 PCI Express 2.0 x16 HDCP Ready CrossFire Supported Video Card - Retail
http://www.newegg.com/Product/Product.aspx?Item=N82E16814102770
(PSU change required)
ASUS EAH4870/HTDI/512M/A Radeon HD 4870 512MB 256-bit GDDR5 PCI Express 2.0 x16 HDCP Ready CrossFire Supported Video Card - Retail
http://www.newegg.com/Product/Product.aspx?Item=N82E16814121276