^he beat me to it, and yes, even I would suggest something like a 7950, they are much cheaper and faster in some circumstances, but that is your choice.
Originally Posted by TecnoViking
I have £400 to spend on an air cooled GPU for single monitor 1080p gaming. I want to ensure the card is futureproof for gaming in the next few years.
For a similar price I can get either a NVIDIA 670 4GB or NVIDIA 680 2GB, which would be the better option?
Final question, are the 'open' style GPUs with 2 or 3 fans better than a 'closed' style with usually just one small fan?
I would go 2gb 670 honestly, I do not think the extra vram helps with the 6xx series slow bus speed. Your card will struggle with the actual games before you hit your vram limit, only a select few games will ever use more than 2gb vram, I do 3 screens on a 2gb gtx670 and I am fine with it. And if you are using just a single 1080p monitor 4gb is far too much. It's far into the 6xx series anyway so I wouldn't get too deep into it.
So my vote is 2gb 680, although the gtx680 is not worth the 100$ more than the 670 in my opinion, its marginally faster.
As for the fan layouts, multifans will keep the cards much cooler and quieter, BUT if your case doesn't have good airflow you will end up heating up the rest of your case. If your computer is cramped like mine is, you will almost certainly need a blower card (one little "fan")
If you see, my mini itx build is the size of a shoebox so I got a blower, but my brother wanted a bigger case so I made him get an open fan gpu.