Well -- Good news and bad news!
1. I was able to flash my 6686 with the roms you provided.
2. My memory clock got stuck on 405Mhz :-( (even during Superposition benchmark).
3. Reverted back to backup of BIOS I had, no problem.
One oddity I noticed was that in GPU-Z, stock BIOS reports memory clock before DDR conversion (1251Mhz). With 11Ghz BIOS, it was at 5501Mhz. I wonder if the card is going into limp mode because it has no clue what do with 5501Mhz (22,000Mhz DDR
)