Depends on the load against the engine at the time, as well as speed and gear. Problem with this is hills, gs and traffic (all variables making your judgement on load hard). Ideally, at the same loading and accelleration gear should make no difference- I expect you could go off the economy gauge to most accurately measure drivetrain loading, are you sure its only one gear? Is that 2nd you are talking about? If it is only first gear you might want to test a bit more... if 2nd it could be the tranny, the 2nd gear band is often the first to go... but that said a new centre bearing is too cheap to argue with... especially if the guibo needs replacement. Sounds like time to pull the exhaust and see... when my bearing went all 3 (RPM, gear and load) all contributed to making the noise (or avoiding it...)