Updating from Geforce 310 in Dell Studio XPS 8100

Hello,

I'm looking to get rid of my 512 DDR3 G310 that came installed with my Dell Studio XPS 8100 several years ago and replace it with something a lot more modern. I know I need to upgrade the psu already so I ordered a CORSAIR Enthusiast Series CMPSU-650TX 650W ATX12V / EPS12V SLI Ready 80 PLUS Certified Active PFC Compatible with Core i7 Power Supply from Newegg because I saw it recommended and heard it would fit in the small case of the Studio XPS 8100.

Now I really need some help with the actual graphics card. Since it's a small case that's going to be a major factor. It has a PCI-e x16 slot. I'm looking for something powerful that can run the latest games and will be good for the relative future. I'd love something with DirectX 11 or 11.1. Also I'm not looking to spend a ton. So something in a midrange price. Any suggestions from anyone who knows the studio xps 8100 and it's limitations? I'd be buying in the US, most likely online. As for the rest of the computer it has an intel core i7-860 processor and 8gb ram running windows 7.