hi i have the same card and i managed to get my core clock op at 1293 mhz stable on 1.200 mv and +400 on memory. i tried to unlock the voltage but without luck. i can send you the bios i modded, it should work.
i can send it when i get home
to flash the bios you need nvflash, you can just google how to use it, there are dozens of videos and threads about it.
if you find out how to push the card further please hit me back