Ooh I see some good reading in your signature links.. I know a fair bit about electricity, but when it comes to hydraulics... not so much.

I went outside to verify this stuff before I got back to you and found something that was a surprise to me. Most of the pool plumbing is 2" including the "spa drain" (suction side from the spa). The spa return, however is 1.5" at least near the jandy valve. The return jets appear to be 2" and there are four! There is a strange contraption (maybe a past repair? I bought the house with the pool) that reduces the pipe from 2" to 1.5" on the spa return. The spa is about 35 feet from the center of the spa to the pump assuming the underground plumbing is roughly straight with some 90 degree bends. So 40' for the furthest return, 30 feet from the closest. There is also an "air" pipe that is connected to the spa piping underground a further 10' from the spa. I guess this is where it gets the air to make the bubbles with, the kids blocked off one of the spa jets once and water came pouring out of that pipe...

Suction Pipe size: 2"
Return pipe size: 1.5"
Jets: 4 @2"ea
Distance from pump to spa: 35' approx

Hopefully that pipe reduction is some kind of design feature rather than a design flaw or (worse) a homeowner pipe repair. Not that it's relevant, but the "backwash" (really just a drain) and cleaner suction lines are also only 1.5" but without the strange coupler that is present on the spa pressure side pipe.

Photos:
exposed plumbing:
closeup of that spa return line: