EVGA are widely perceived to offer the best warranty support. If the card goes wrong after a few years you won't get any nonsense with "partial refunds" being offered at low values. EVGA will replace the card like for like, or provide something better.
As for the 4GB version, it is unlikely to offer additional performance unless you game at extremely high resolutions and settings (mult-monitor). Some games may se slight benifits @ 2560x1600, but not many. If you are sticking with a single monitor, it is probably worth sticking to 2GB.
One last thing. Whilst EVGA offer great support, graphics cards in general are unlikley to fail, so the chances of using it are slight. It is not worth spending a lot of extra for support you are extremely unlikely to need. Go for EVGA if the price is good, but don't spend £30+ extra for it.