What you want to look for in a gaming laptop is pretty much just the gpu. Around your budget, you should look for a 540m or 550m. Anything fast like a 555m + graphics card will cost you $1,000+
From the stats alone, I would say throw in another $50 and go for the 550m with 17inch screen.
But if you really just want 15.6 inch screen and medium graphics settings, the 540m laptop will be cheaper and also give you a good 60 fps from the stats. You can look up a Radeon HD 6650m gpu laptops. The HD 6650m is just slightly slower by just a small bit from the 540m, and I think laptops that come with the HD 6650m is a little bit cheaper.