I think the 400' for flap retraction comes from people using the same logic about keeping the configuration the same, but not updating it after 1970 when aircraft started having the performance to get higher before having to accelerate!
Tom, my comment about the flaps helping the initial climb was from a handling perspective, not a performance one. All your calculations may well be correct, but that doesn't alter the current requirement, and climbing at 190 (or other suitable speed for different types) is compliant. There is an entire thread over on techlog about whether using reduced thrust for a NADP actually increases noise levels, but it is entirely academic.
Effectively at the moment, to use a car analogy, you are saying that because my car is more efficient at 50mph in 5th gear than it is at 30mph in 3rd I should ignore the 30mph speed limit. Unfortunately, the fact that your reasoning may be correct does not make the speed limit go away!
Therefore I will continue to follow my company's procedure which is compliant with the rules.
Happy flying.