6950 unlocked makes nigh on no difference and it is not even remotely as quick as a 580 even at stock...
I did say unlocked and @1GHz.
An unlocked Toxic@950MHz:

'Overclocked 1536 BIOS Performance Summary
Wow, what can you say? AMD's Radeon HD 6970 market ranges from $340 to $380. NVIDIA's GeForce GTX 580 market ranges from $420 to $600. Our SAPPHIRE TOXIC HD6950 sells for $269.99. After overclocking the 1536 BIOS, it also out performed both of the price superior cards. A much cheaper price and comparable performance, very impressive!'
Regarding unlocking the shaders, admittedly it's 'not much', but sometimes the 570 outperforms the 6970 by 'not much' and vice versa, every little helps, especially when it's free.
A pair of 6950's is quicker than a 580 and still outperforms a 7970 in a lot of games.
And that's why I'm keeping my cards!
A pair of 6950's especially when unlocked to 6970's @ 1GHz go way, way past a 580:
From the ***Official Unigine Heaven 2.5 Benchmark Scores*** thread:
Fastest single(most likely oc'd and maybe under water) 580: No. 55 Jazzerman (GTX580) - 1609
My AC Extreme air cooled 6950>70's@1GHz: No. 22 tommybhoy (6950 Xfire) -2269 (which I think is the fastest air cooled 6950>70 results in the thread)
1 year ago these cards cost less including 1 cooler(as I already had one) than the cheapest 580 at the time.
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