Thanks Genghis,
In answer to your first question, +/-2.7% is an approximation for the movement of the aircraft CG following fuel slosh from a +/- 10 deg pitch change. Good point about stall entry and recovery, will look into those.
Some more info. Have done a basic analysis which seems to indicate that their is no critical slosh level (33% full, 50% or 66%). Seem that whilst the fuel CG movement is greater at lower fuel levels, the mass is also reduced. Thus the effect is the same as for a greater fuel volume moving a lesser distance.
Look forward to more test ideas.