Unlocking to 6970 won't be very easy these days. Like the MSI R6950 Twin Frozr II which has removed the BIOS switch. See here:-
*cdn5.tweaktown.com/content/3/9/3900_08_msi_radeon_hd_6950_2gb_twin_frozr_ii_video_card_review.jpg
(Image from TweakTown)
Even XFX has done the some. There are several failed reports of unlocking in the newer batch of cards. Some others are reporting high temperature (both idle and load). I got a feeling that just like all the retail 6950 1gb (Sapphire, XFX, HIS) uses the 6870 PCB basically these dirt-cheap 2gb cards are also using some other modified PCB rather than the original one which is somewhat preventing the cards to get unlocked stably. So if the Sapphire card is one of the earlier batches, then its really nice. Heck, its even priced lower than my 1gb card.
Before purchasing just make sure you check out the dual BIOS switch actually exists to save some pain in future.
In any case, the 6950 is a hell of a card in its own right. If it can be unlocked to 6970 it is a added bonus IMO.