Tony
If the FMS shows FL 409 as the MAX ALT, then the aircraft with autopilot and VNAV engaged will level at FL409. Any attempt to climb above FL 409 by disengaging the autopilot will change the pitch mode to V/S. Changing the CG is a legitimate method of obtaining an accurate MAX ALT. From the conditions that you describe, with no centre tank fuel, the CG would be about 23% (from experience).
You stated the pages that were selected when the ATC request was made. If you need to wait until the request is made then you are not thinking ahead of the aircraft. At any stage of the flight you should know the MAX ALT, as well as the 3-eng driftdown height, the MSA and the nearest alternate. The pilot who says 'standby' when asked if he can climb is the one who is flying with his aircraft rather than ahead of it.
However, if any of my colleagues were unhappy about a climb decision, then I would explain my thinking to them, and consider the alternatives. If they were still unhappy then I would change my decision and descend, as I might need the guys advice at a later stage, and I would want it to be forthcoming.
If we are assigning CRM points here, then I think that the two of you are about equal. It is a shame that the captain was not prepared to give you the benefits of experience, but I have certain doubts about your attitide to him. I have been flying the 747 for 27 years. Some of my knowledge was obtained from books, and some by experience. I hope that I am able to pass on some of the experience, just like the previous generation did to me. I'm sure that most captains feel the same, please just give them a chance.
Airclues