Much research led me to this card, yes you can still pick up the older 6870 and this newer card won't give you much more gaming wise but it will use less power, give you more multi-monitor configurations and also give you more options in the future (using this card in crossfire with another 7770 gives great results for not much cost).
After physically installing I booted into Ubuntu 12.10 which picked up the new card and worked flawlessly. I then booted into Windows 8 and came across an issue, the fault lies within Windows 8 and not this card.
If, like me, you install this with Windows 8 using HDMI and find that after a 30 seconds or so your screen goes black here is my solution (it may work for you, it may not, I accept no responsibility):
Windows 8 will detect the new card but the drivers it uses do not support HDMI very well, hence the screen going black. The drivers in the box only work up to Windows 7 so I shut down, connected my PC and Monitor via VGA cable then downloaded and installed the latest Windows 8 drivers from [...], then shut down, connect PC and monitor via HDMI and voila! All works well.
Hope this helps.