Need help with these choices please

Hey guys I'm hoping someone here can help me really because I can't find anything to help me make my decision any easier. My Computer is archaic and isn't upgradeable so I'm looking at buying new. This time i'd like to be semi mobile with it so i'm looking at gaming laptops, sub £2k gaming laptops.

I'm looking currently at Alienware and XPS machines and keep coming unstuck on the graphics card configurations obvioulsy each adding an extra cost to the total cost of the machine.

Here's my dilemma;

A) The XPS comes with Dual SLI 51Mb nVidia 8800M GTX cards [Inc in price]

B) Alienware will ship with Dual 512MB ATI Mobility Radeon HD 3870 – CrossFireX Enabled cards an extra £193

whilst the second Alienware offers one of the following

C)
(i)Dual 512MB NVIDIA GeForce Go 8700M GT – SLI Enabled an extra £229
(ii)512MB NVIDIA GeForce 9800M GT an extra £304
(iii)Dual 512MB NVIDIA GeForce 9800M GT – SLI Enabled an extra £763
(iv)512MB NVIDIA Quadro FX 3600M an extra £343

I know that Option A is old tech but is it that old that it's not worth considering?
Option B is using ATI cards are they that much worse than nVidia as the price would suggest?
With regards to option 3. . . I know that the (iii) config is the best or thats what the price would suggest at least, does it really offer £800's worth of performance over say config (i)? or would I be better off settling for a single card and having only 512Mb dedicated to my graphics.

Any help is greatly appreciated, thanks!