747FOCAL,
I also fly the 747-400 and according to our manuals from boeing, "flight tests and analysis have proven the change in take-off roll due to rolling take-off procedure is negligible (less than 50 FT) when compared to a standing take-off". We are directed to set 1.10 EPR approximately and allow the engines to stabilized momentarily before pressing the TO/GA switch.
Are you possibly waiting too long prior to press TO/GA to burn 600' - 700'?
Boeing states the reason for the rolling take-off's as it expedites take-off and reduces the risk of FOD.