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If I was buying right now I would buy the GTX 780 MSI gaming
http://www.overclockers.co.uk/showproduct.php?prodid=GX-209-MS&groupid=701&catid=1914&subcat=1341
or for £20quid more The big brother Lightning
http://www.overclockers.co.uk/showproduct.php?prodid=GX-207-MS&groupid=701&catid=1914&subcat=1341
290 is fantastic but has a fairly loud cooler, so at present could do with water cooling or wait it out for a custom cooler (6-8 weeks).
780 has custom coolers already both perform within whiskers of each other with the OC version of the 780 comfortably beating the 290 and X in most games.
Mantle is coming and it is all speculation on performance gains, so if you are in no rush, wait it out till December/January to see what is what.
If I was buying right now I would buy the GTX 780 MSI gaming
http://www.overclockers.co.uk/showproduct.php?prodid=GX-209-MS&groupid=701&catid=1914&subcat=1341]

290 CF now with water cooling = Maxwell performance at 780 Ti price
290 cf watercooled would cost far more than a 780ti.