My question is: so what if the Toxic 6950 doesn't unlock? Comparing straight 6950's to 6970's, the difference is right around the 10-15% range in average fps anyway, depending on the game. A 6950 is a heck of an upgrade already, let alone one that comes pre-overclocked, and even has some headroom for more. Unlocking would just be the cherry on top of your dessert, not the actual meat and potatoes.
For around $270 after rebate, that's an amazing deal to beat for close to (if not, better than) GTX 580 level, which significantly more than what you are looking to spend. If you want the guaranteed unlock for meager performance gains, you would need to spend the extra money on the 6970. In my opinion, a $320 Toxic 6970, that dances back and forth with a GTX 580 at stock factory clocks, is still a great deal.
You really can't go wrong with these Sapphires.
These cards are actually making me consider switching my 580's out for them, thanks to having good waterblock support.