Limiting factor is going to be your power supply in how many Watts it can supply and if it has any PCIe 6 or 8 pin power connectors. Also what length card will fit in your case.
There is an article on Toms Hardware on will Mass Effect 3 run on my PC here >>
http://www.tomshardware.com/reviews/mass-effect-3-performance-benchmark,3143.html
Also Tom’s runs a regular what’s the best graphics card for £/$ here’s the March edition.
http://www.tomshardware.com/reviews/gaming-graphics-card-review,3107.html
At the end of the whats best there’s a graphics card Hierarchy chart for a v/rough comparison, for example by choosing X card are you jumping up a few levels in performance.
I think the AMD 77xx series look a tasty option at the moment the 7770 is at 6850 performance and draws less power, the 7750 doesn’t even need an extra power connector on it.