We design mining equipment systems that pump slurry under pressure for thousands of linear feet at varying amounts of lift, usually do not pull vac (our centrifugal pumps don't like to prime). Centrifugal pumps have more in common with a fan than piston pumps do. The idea is that there is less work being lost to friction that come from higher velocities. Immediately after the pump we also put a reducer, actually as an increaser, to further slow the velocity to just above where the slurry remains in suspension. Through many years of experience, this recipe has proven itself over and over. Less power is used and pumps and piping lasts longer. That's the way it's done (correctly) in the mining industry.While you are right, the larger pump would use less voltage to achieve the same vacuum power with a bigger piston. It’s not just motor size, think about woofer size, the bigger the woofer the less power is needed at lower frequencies.
Also less heat and less resistance, bigger bearings having less restriction. It all adds up but I imagine the biggest effect comes from lasting longer and needing less maintenance.
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If given the choice between too small, theoretically perfect, or too big, it is better to go somewhere bigger than theoretically perfect.
I hope I was effective in explaining the reasoning.
I know that this talk of pumps was not intended to say that dual fans will have no benefit. It was an analogy. Perhaps I should not have mentioned it because of the distraction potential.
Spinning 2x 92mm fans at 1/4 the speed will flow similar amounts of air in cfm (not static air pressure which is rather unimportant in an open flow situation that cooling requires), will use half the power, the fans will last longer and be nearly silent, all benefits.