It could fry you bios or leave your baord unstable. With that said are you still going to try it? I have a BE6 and while I was upgrading the bios, way back when, the update crashed on me. I talked to a rep over the phone, yes I live person, and he instructed me how to get my bios back. Don't know if you want to risk or not.
Another idea would be to send an email to abit support with the following:
"I accidently flashed my BE6 board's bios with VERSION of the BE6-II board's bios release. So far everything is working fine, but wanted to know if I shoud flash this back to the BE6 version XXX or is it okay to leave this alone?"
Give it a shot! Let me know what you findout. I have a BE6 also (ATA66 controller fried from OC).
JoeCervi