Thank you, Mark, for the calculations.
Without a flowmeter or a vacuum gauge I can't verify these numbers. However, the currents produced at the return outlets
indicate a strong flow. Can one have a "feel" for the flow rate from the intenisty of these currents? I can post a pic if this can help.

Suppose I want to get a vacuum gauge, I have two questions:
1. Where can you get it, and would it fit the hole in the skimmer?
2. Is there a way to comensate for the suction pressure drop between the skimmer and the pump? I undewrstand that what you need is the actual pump suction vacuum.