I have 2x HIS v64, 6x gigabyte v56, 4x sapphire v56, 4x XFX v56. They are all identical cards that was made by amd. One v64 has brown pcb. Some stats:
v64 obviously works without issues @ 1400 0.9v / 1100 0.9, i think 99.9% of v64 should works fine with this config
13/14 v56 flashed to v64 bios, one v56(gigabyte) crashes after some time with v64 bios even if set to 1200 0.1v core 800 0.95v hbm, but works fine with own bios @ 1350 0.1v 1000 0.95v hbm
4/13 flashed v56 works @ 1400 0.9v (1 gigabyte, 2 XFX, 1 sapphire)
7/13 flashed v56 works @ 1400 0,925v (4 gigabyte, 2 XFX, 1 sapphire)
1/13 flashed v56 works @ 1400 0,935v (1 sapphire)
1/13 flashed v56 works @ 1400 0,965v (1 sapphire), unable to set lower voltage but temperatures are same as 0,9v cards (sensor bug?)

for custom cards sapphire looks very good but has 3 8-pin