Has to be a 2006 or 2007 ECU. There's really no way to diagnose it other than swapping it with a known good. It's more of a process of elimination to get to that point, which you've already done. It's just a hypothesis and I really don't know the pathology, how much of an over-volt it takes to cause the damager, or any other details. Only a lot of history and testing to show the STVA is good, and reports that the bike just suffered from other electrical issues. Just a lot of reasons to think the ECU is the issue.
The other issue I've seen is a STPS that has cross faulted. Usually that causes a different behavior that a fluttering. I would say your ECU is the faulty component.
Same problem as mentioned above. STVA checks out good abot 7.4ohms then checked the stps also good readings open and closed butterflies. What I'm wondering is if it's possible to use an ecu from an 09 an long as you get the wiring harness for that year also? Because the ecu for 06-07 gsxr 750 seems to be hard to come by.