As far as bunching goes, surely that is best avoided by everyone flying the same speed. What that speed should be will vary between aircraft types and operators requirements. Maybe the operators should be canvassed and then a compromise speed be arrived at. 280kts gets my vote, its a middle of the road speed with room to slow down or speed up comfortably by most types and closer to econ climb speeds than 250kts is. BTW this is the first i've heard of it as well.