scaryjim
Re: Need Advice
Will you be upgrading your monitor again in the next three years? If no, thenforget SLI. In fact, since you've got a large enough budget to buy any current single GPU card, forget SLI altogether. In 12 months you'll not suddenly find a GTX680 can't power a single 1080p screen. There won't be some massive sea-change in graphics technology that means game engines are making your £300 graphics card weep.
Here's what you do: buy your choice of GTX670, GTX680, HD7950 or HD7970. They're all excellent cards for gaming at 1080p. It sounds like you're set on over the top performance, so probably best go for a GTX680 or HD79790. They'll both give you around 60fps in most modern games at 1080p. Don't bother with the 4GB version of the 680, running at 1080p you won't see any difference at all.
Then, in 12 - 18 months time, sell your current card and buy the fastest card from that generation that you afford. That way you don't have to worry about lack of support or questionable scaling in any games, you'll get a better feature set, probably lower power draw. Chasing "SLI later" is always a bit of a dead end - by the time you've got your second card for SLI there's a reasonable chance there's a single card out there that's faster. You're better off spending your money getting the best experience you can now, then worrying about what upgrades you can afford when you actually need to upgrade. There's no such thing as future-proof in computing: may as well focus on the best experience you can get right now