Well there's your problem!
You got a beastly 5850 and not a very good 6950!![]()
No, I've got a reference 5850 with a Zalman cooler and a non-reference 6950, Twin Frozr III PE OC. I wouldn't call either a cheap card.
Stock for stock there isn't much difference, overclocked vs overclocked there is even less.
These cards would be great if they cost £150, with current prices I wonder why anyone is buying graphics cards these days.
Got my 5850 on launch, £200, almost two years later it was half this price.