Every rotary vane gast pump I have looked at specs. on are pressure or vacuum. If the specs. list so many cfm at so many psi, that is for the pressure pump side, I believe, and someone plse correct me if I am wrong, that vacuum pumps are stated at so many inches of Hg(mercury) they pull. This pump rotary vane should be quieter and draws 1/2 the current both of which you said were important. It is probably a surplus from C & H sales or some other mil. surplus store. They are 90's ventage, but very similar to current production models. Just make sure the vanes are the same as current productiion, for replacement consideraations.
I am discussing your original pump that you posted. It delivers more air and runs at 1/2 the current of the second one. Either one will deliver plenty of air to your size pond.
