i looked into it and found out that the stock 6800GT has a 1.3v vcore and the ultra has a 1.4v vcore. i also saw people getting much higher overclocks with their bios flashed too.
It's not common practice and one can easily fry something. You can do it, that's fine, I just choose not to, I'm not telling anyone NO DONT DO IT, YOU'LL DIE! but generally there are more risks of instabilitis associated with it
But it doesn't offer you and extra bandwidth. Jaksback has done 3dmark03 with it at 72MHz and at 66MHz and it gives the same thing.
That is right. There is no difference in performance. I would never clock the BUS to 74 MHz intentionally. Like I mentioned above though... I had no choice.