[supergonzo]

These engines all used the same intakes and exhaust, the 70-71 were in heavier cars.
However:
The best breathing heads were 70 400 RAIV's
Followed by 69 400 RAIV's
Next would be 71 455 HO heads, slightly less flow on intake
Finally would be 72 455 HO heads, even slightly less flow in exhaust area. Pontiac engineers knew at this time, compression ratios were falling, and were trying to get as much torque as they could out of the heads, and not worry about upper RPM air flow, as the 400 RAIV's were built. The 455 HO's also did NOT use a RAIV cam although the heads were similar they used the earlier MUCH milder 068 (tripower) cam. Again due to emissions and better low rpm cylinder fill with low compression on those heads.

A 455HO does have a lower rpm peak than a 400.However
The 400 RAIV's were underated, as several magazine dyno test have been done (even recently) and showed in stock form they produced 400-420HP.
The 455 HO with its emission friendly cam has had dyno test in the neighbor hood of 360-370HP, if I remember correctly. The 4400 peak HP rating is definitely too low, and probably rated that way on purpose, to satisfy then very restrictive insurance rules.