Yes that 4850 is a good choice...
Another very good alternative, cheaper equally good and with Free shipping...
HIS H485QT512P Radeon HD 4850 512MB 256-bit GDDR3 PCI Express 2.0 x16 HDCP Ready CrossFire Supported IceQ4 Turbo Video Card
http://www.newegg.com/Product/Product.aspx?Item=N82E16814161244

But just a heads up...though that 4850 would be suffice for that resolution, you might not be able to play all the current games @ max settings...You can upgrade to this card, which would best suit that resolution...but would be about $150 with Free Shiiping + $10 Mail-In-Rebate...
SAPPHIRE 100259-1GL Radeon HD 4870 1GB 256-bit GDDR5 PCI Express 2.0 x16 HDCP Ready CrossFire Supported Video Card
http://www.newegg.com/Product/Product.aspx?Item=N82E16814102801