First off here a little something about the unlock
There are two types of 6950 unlocks:
Type 1 unlock: Shader increase to 1536 units (same as the 6970)
Type 2 unlock: Complete BIOS flash to a 6970
The type 1 unlock is almost risk free and can be achieved with almost all the 6950´s.
The type 2 unlock on the other hand is a bit more risky because due to the full 6970 BIOS flash also the timings of the 6970 and other settings which are different will be applied.
To some cards that ultimately can lead to card failure or mailfunction.
Further marginal differences can be seen here:
But be advised that the Type 2 unlock only yields about 1-3% performance increase.
Wheter the Type 1 unlock + stock 6970 clocks have shown to yield the exact same amount of performance a normal 6970 would achieve:)
So according to those results one could imply that a Type 1 unlock + stock 6970 settings would upgrade a 6950 to a full 6970 performancewise even though other settings or structural differences are unequal.
Both types of unlocks will void your warranty if something goes wrong so be sure to bare that in mind when doing it.
There have not been any long term studies about the affect of the unlocking process and further causations yet.....but I am confident to say that nobody has encountered any problems yet:)
So I personally would advise you to leave the unlock be as it is not included in the warranty and just overclock your card 5-10% higher ...thus a higher overclock should be able to not only compensate but even exceed the performance boost the unlock provides;)
And if you must have an unlocked card at least wait until we know more about its long term affects:)
I would also like to refer you to my thread in which similar questions and all advantages/features benchmark results,performance comparisons to other cards including all designs etc etc should be displayed and answered:)http://www.overclock.net/nvidia/984836-gtx-570-sli-vs-amd-6950-a.html
Here the full guide + tips on unlock from TechPowerUp:http://www.techpowerup.com/articles/overclocking/vidcard/159
Now you should be pretty much informed about the unlock.
Here a little bit about the unlockability of the 6950´s out there:
If a card unlocks or not is depending on wheter or not it has been laser cut to make it impossilbe for software to unlock the unfunctional units.
Another crutial part of the unlock is for the card to have a BIOS switch so in case somthing goes wrong you can always flash to the second BIOS.
Basically 90% of the tested Twin Frozr III cards unlocked fine there are already some newer laser cut products around so be careful to check the arrival date
of the card at your local retailer before buying it to ensure it couldn´t have been laser cut yet.
Hope I could help:)
Anything earlier than March 15th should be fine I believe:)