Colin, I would not be surprised at all, if you did not hit the bulls eye here, smack bang in the middle /--)
So much so that I have adopted this as my primary working hypothesis. I will do some research on what's involved in (driver) signing in general and let you know if I find something interesting. But I have one question for you NForce750i owners which I can't look up. Could please look at your various installs and post the driver info? If you could post build, architecture, publisher, version , date that would be most helpful. Thanks already.