When I tested the 6bbl FAST motors, we always ran with the air filter in place, since that’s how they are run in the car.

On a mild 446 build similar to the one in the link, I tested the filter base with no element or lid, against the complete filter.
The complete filter was down pretty much everywhere.

The bsfc numbers were actually slightly better with the complete filter on, but the power was lower.
With the element and lid installed the motor was using about 10-15lbs/hr less fuel at the upper end of the pull.

These are back to back tests done 4 minutes apart....... never even shut the motor off.