Hey there I'm planning on getting this desktop sometime in the next few months. My main usage of this computer will be for gaming. I know that Intel Hd Graphics or any of the ones that i may upgrade to during purchase( 4GB Nvidia GeForce GT640 [DVI, DP, HDMI, VGA via adapter; DX11] or 2GB Nvidia GeForce GTX 645 [DVI, DP, HDMI, DVI to VGA dongle; DX11]) aren't all that good for gaming. So I was wondering what graphics card should i upgrade to and why? My price range is about 100-200 dollars. Thanks!