we should not advance any thrust levers until we go to MCT if using fixed derates
That raises a point in philosophical difference. Indeed the takeoff thrust can be less than the continued climb thrust. While this might be fine from an engineering standards point of view, I prefer Wal's approach with his QF buddies. He related a tale about a crew's complaining that the F/E had pushed up the throttles to achieve METO/MCP - after a few seconds' thought, he concurred and, thereafter, the minimum flex level was climb thrust.
Many of my colleagues would love that restriction as it is allways somewhat funny to see an increase in thrust on climb-thrust reduction. The 737 offers two fixed reduced climb thrust settings based on max rated thrust. So using derate take-off thrust combined with assumed temperatures can lead to quite substantially less thrust than the lowest (climb 2) climb thrust setting.
Are you sure your full thrust Vmca is below your fully derated V2?
The mutts, OSs, and JTs of the world like to keep the Vmca bogeyman in the thought processes just so that the newchums end up with a rational respect for those low speed lines in the sand. However, the line pilot should adopt a pragmatic approach - Vmca, generally, is way below your V2 and not a major concern unless one mishandles the failure grossly.
Sadly we do not even get any tables concerning Vmcg/a anymore, they were all removed because "the software only provides safe combinations, you don't need to worry", but on the other hand we get told "do not ever advance thrust levers if using a fixed derate".
including V2 which can vary by as much as 40kts
While I can't comment on the 40kts as that would be specific to your particular bird, there is no problem with V2 varying - perfectly normal. However, you don't bring V2 below V2min for the day.
Exactly what i was trying to say, thanks for clarifying it. It seems V2 was rather fixed for aterpster when in reality it is a very flexible thing within its limitations.
By the way, with V2s as low as 1 to 2 kts higher than Vr it will be an interesting example in precision flying to keep that speed during rotation and beyond with the kinda lowish rotation speed required for stretched bodylength-aircraft (738/9).