Hello,
if you're inclined to go with dell, Alienware M17x should be plenty (or they had 18x which was an 18" model, not sure if its still in business)
usually comes with a GTX560M stock I believe.
Other options that might give you same hardware for cheaper are
Asus G73/74 series
Sager NP8170
MSI GX780
typical minimum hardware on gaming laptops as follows:
i7-2670qm, 8Gb DDR3 ram, GTX 560M or ATI equivalent, 500Gb+ HDD (7200rpm)
you can obviously get a better gpu for models that allow customization and also consider an SSD instead of HDD.
If you need an idea of what the performance of GPU is in-game refer
>here<
if you'd like to get approximate pricing on certain models refer to following websites:
www.xoticpc.com
www.newegg.com
Best of luck, hope this helps you pick what you want.
Ask if you have more questions