"I believe when talking gallons per acre, one also needs to include speed, and width....."

Yes.  The speed and gpa has not changed much, but the planter is twice as wide now as it was back then.  That means I'll need twice the gallons per minute from the pump.  According to their literature, the smaller variable displacement pump pump at 550 rpm would get me from one to 30 gallons per acre (40 foot width).   Given the higher gpm from the pump, the faster spinning and smaller displacement of the John Blue, and perhaps the double acting piston design of the John Blue, I would expect to have a much smoother flow than what I got from the Hypro back in the '80's. 

The Hypro was working well on a 28% sidedress bar.  Back then I had hoped to use it on the planter as well, but it did not work out since the only way to reduce it to five GPA was to use slower sprockets.  It would seem the vairiable displacement of the John Blue would be an advantage.

I use a John Blue for NH3 and agree the durability is far better than the electric pumps (and associated gadgetry) on my planter.   It also does a good job getting the desired rate applied.

-Just a little leary about being able to get an even flow when applying a small amount to the seed furrow. 

Thanks to you and others for the replys.