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To early to say yet?
Reason it won't cost £700 +, its "early no competition no price wars" pricing. AMD are cashing in:
Actually, it will very likely come out near to £700 ($850 = £546; +20%VAT = £655, plus vendor mark-up). Afterall, it was the same with the 7970 - using the same calculation is converts to £420, plus vendor mark-up (most of the cheap ones are hovering around £450).Won't be remotely close to £700, and, very difficult to say. While the 7970 is VERY clearly TDP limited and can overclock like a beast, at top clocks you're looking at 300-350W for a 7970 core.
The 6990 was launched at around £500 here, but has fluctuated with the exchange rate between £500 and £600. The 7990 is the logical replacement, so should be priced similarly (assuming NVidia offer some real completion with GK110 or whatever). I expect launch pricing to be around $800 / £600. By then the 7970 will likely have dropped significantly as well (as said above, it only holds a premium because it has no competition yet).
So, 7950 for £250, 7970 for £350, and 7990 for £600, dependent upon NVidia releasing decent copetition. If Kepler crushes AMD, prices will be cheaper still.