comes without OS (+80$). you can get this machine with 675M for around 1420$. 5 hours will be the top it will run on a battery. best performance to price ratio and highest performance you'll get for 1400-1450$ currently.
2. If you can compromise and play BF3 on high settings but not the highest ('ultra'), than GTX 660M laptops will be good for you too, like the Lenovo Y580 which offers great performance for the money, 8 hours in light use (4-4.5 surfing constantly / DVD): http://www.gaminglaptopsjunky.com/lenovo-ideapad-y580-1...
i agree with 77's idea Y580 is designed for normal gaming palyer rather than soem extream ones like alienware and it is a little conradict to get one whith a high performance and light weight
and 610 is almost imposible to afford bf3
580 is just the mudium for you using the gtx 660
and try the lenove offical website they sometimes offer discount in the particular time