Hi If based on this site's testing the GDDR5 in 6950 and 6970 are set and tolerated at the same 1.6v! So flashing the 6970 bios should not make an effect of killing it!
http://ht4u.net/reviews/2011/msi_r6950_twinfrozr_2_test/index7.php
http://ht4u.net/reviews/2011/msi_r6950_twinfrozr_2_test/index7.php