I researched this awhile ago when looking for a dry sump system for my current engine.The actual Missle users I talked to told me that gear wear is the same as if you were driving a normal wet sump pump.In other words they last as long as any other bronze gear intermediate shaft.They are nicely made and I heard no complaints.6-8 in vacuum is what I was told is normal for these pumps to make by themselves.
All that being said, I went with the Dailey setup like in Fred's picture.Mine is a 5 stage with the pump section at the rear of the suction sections.Dailey uses a roots type lobe for the pump/suctions.75-80 psi at 9500 rpm hot with 0w10 oil with 15 in vacuum regulated,will pull 20-22 with no regulator.I am using their pan and a Steff's tank.It's nice not having the extra plumbing on the left side of the engine.That is the main reason I went with this setup.3 lines,feed,return and pressure to the block.
I hope this helps!