Since that is a non reference card, take a look at update 2 (http://www.techpowerup.com/articles/overclocking/vidcard/159). This is the method I used on my non ref.card. You do not want to flash back with a reference bios from what I have read. Hope this helps.
Greetings from a new member. I just received my HIS 6950 IceQ X Turbo 2GB from Newegg. Using RBE and winflash, I had no trouble getting the additional shaders unlocked. The original overclock at 840 is there and all running cool and quiet. The card is non reference and had not bios switch. Yes...