Get the GS60 Ghost Pro!! I have one, and its brilliant! So light and portable! I've come from a heavy alienware, and this is definately the way to go! But that said you pay for the privilege of weight reduction! The GT60 with GTX 870m and i7 4810MQ is £1099. The GS60 with GTX 870m and i7 4700HQ is £1400.
But why not look at the gigabyte ones too? The new P35W can be had with i7 4710HQ, GTX870m with SIX GB of RAM, 8gb RAM, 128Gb SSD and 1Tb HDD, AND a removable DVD RW drive for £1259.
I think the build quality is a bit cheaper as its plastic, not MG-Li like the GS60. but bang for buck is outstanding.