GTX 770M versus Radeon 8970M

Upendra09

Distinguished
I am considering this laptop from Toshiba

http://www.toshibadirect.com/td/b2c/cdetland.to?poid=2000098978

with the following specs:
i7 4700M
8GB DDR3L 1600
GTX 770M
500GB HDD
Intel centrino n-2230
Win 8

there are other laptop that I've looked at, like a Sager from Xoticpc which is slightly more expensive but features the Radeon 8970M with 4GB VRAM, so my question is, is the 8970M worth buying over the 770M?

I used comparison websites like GPU boss and game debate to see a comparison but they all use the 2 GB variant of the Radeon

I'll be playing Need for Speed: Most Wanted(2012) preferably at full HD and highest graphics settings as well as Need for Speed: Rivals

I understand hey both will work just fine with the games but which will also last longer in terms of being future proof? I need this laptop to last 4 years so......

Thanks for the help!