Ported intake gain?

As referenced in the port matching thread here, engine masters did a back-to-back-to- back test of three intakes, super Victors on a 550hp small Chevy. Stone stock ootb, port matched, and Wilson ported.
Ootb 546hp
Port matched 554hp
Wilson ported 564hp.
Ootb manifold was $375, Wilson was $1000, so $625 for 18hp.
For a milder motor I would expect milder gains.
Edit: forgot to mention, ALL gains were above 5300-5400. Most gain (more than at peak) was at 7000.
2nd edit: tried a $100 tapered 1 1/2 spacer on the Wilson, made another six hp.