Going by that chart, the 6950 is only 13% more efficient than the 5830. For that money the 5870 looks a lot better.
But try to even FIND a 5870.
Yeah there are not many out there, if I wanted to travel to a store ~150 km away I could get 2 for C$220 each but I don't want to piss off my landlord with the power bill.