Not really where I was going.
The “300cfm” is useless info without the test pressure.
More test pressure = more flow.
The reason the cubes have the potential to make more power using the “same” top end as a smaller cube build is....... the bigger cubes create a larger pressure drop, resulting in more air being consumed.
Mix in the appropriate amount of fuel with the added air........make more power.
For most of the typical stuff people build, this is how it usually shakes out.
Well....... for me at least.