Interesting - my cards are v277-38SB as well. Either way, it seems to reason these cards can definitely be flashed and undervolted.
By the way, were you trying the 1137 voltage?
I'm glad you got it to work.
I'm going to try undervolting to 945mv tomorrow.
I am having a problem of some of my cards crashing when running cgminer the cards I have although the outer box is all the same, on the serial# some are v277-38SB while others are v277-36SB now I changed the bios on both to 015.040.000.000.003435 (113-C3865000-X77) as I assumed all are pretty similar ....I have another rig again same cards but somehow works great all ok and mining is great...really confused why I am having problems with second rig where all cpu, mobo. ram etc etc is all the same ...any ideas / help would be welcomed.