1515blue,
VMCG has nothing to do with weight, its pressure altitude, temperature and thrust rating and the resulting aerodynamic forces over the rudder.
The VMCG speeds that i used above are about right for a B747-400 using Maximum Thrust of the installed engine at sea level/ISA and then Derating that engine by 10%. Therefore the VMCG is REDUCED as the engine thrust rating is reduced.
Please note that I'm talking about FIXED DERATES, although we are allowed to do Assumed Temperature thrust reductions, we always base the VMCG on the Actual Temperature.
Now if you really want to get confused, ask J_T about crosswinds and VMCG....
Mutt.