The Sapphire Vapour X edition is essentially a card with a good cooler than any other
I dont think it is worth getting beacause if you you have a good case with, say, a 120mm fan, you wont feel good spending extra cash on the Vapour-X edition
I suggest you to for XFX 5870
with Double Life Time Warranty
I would go for the Vapor-X for sure. It comes factory overclocked and with its better cooler you can push it even further. If you really want a double lifetime warranty or you dont plan on overclocking, then the XFX is a fine choice.
Also, for future reference. When asking a question about video cards you should post it in the Graphics and Display section on the forums. About just as many people look at that board as the CPU board.
The Vapor-X version has a more efficient aftermarket cooler and is slightly overclocked.
I personally would say it is not worth the extra 50£.
Such a minor overclock can be done your self in about 10 seconds.
As the OC is so low (20Mhz core, 50Mhz mem) you are virtually guaranteed success.
The stock cooler on the 5870's are actually very good and quite quit (especially if your case has good ventilation).
I have my 5870 running at 900/1300 and it is quite quiet, even under full gaming load.