As you've said, all the increased height of 5mm of the runner port is at the top. If you drop the manifold you end up with it at the bottom instead! What does that achieve in matching? It only moves the stepfrom the top to the bottom.

The inserts are there to prevent over stressing the manifold with the bolts/studs/nuts and fatigue, as with any composite manifold. How do you prevent that when they are removed.

The standard manifold (pre-2003) actually flows very well with mild porting, and although not necessary unless trying to exceed 180bhp, can be fitted with a larger TB easily.

Is your opinion of ST170 'flow' empirical, or do you have measurements? In the short runner position it is obviously better at high revs, but thats a resonance issue, not static flow effect.

Martin