Another couple of thoughts - many people are making the argument that with all of the high flow, relatively low cost internal powerheads that can be had these days, having multiple return lines is really not that much of an advantage, if any. In the old days multiple returns helped with mixing water, but one Maxspect, Vortech, etc will move a lot more water around your tank than the return ever will. Greatly simplifies the plumbing. Unless you want dual returns for other reasons, might consider this. My own experiences suggest that the thought is right, the powerheads do a lot more than the return....
The discussion about return lines is interesting, I talked a bit with the support at Reeflo before getting my new pump, they also suggested that to really get the max out of a pump, especially if there are bends in the line, it will help to go to larger pipe. However, if the distances are relatively short (ie your sump is not in the basement) and any bends are gradual, it is not necessary to do this and reducing it somewhat is fine. Flexible PVC is your friend here....
btw, I love that Reeflo snapper/dart gold return pump I ended up getting, I'd recommend to anyone... My sump is in my basement, about 8 foot head with some twists and turns. With 1.5" pipe up into the tank stand, then 1" from there into the tank, I get over 2000gph when opened right up - not much loss from the specs of around 2400. I normally run it at about half that, with flow also going to my frag tank and fuge... I also have one of the new jecods you mentioned on my freshwater tank, they have improved a LOT this version, quite a nice pump.
Finally, if you are going to run any filter canisters, calcium reactor, or anything that might have changing resistance and therefore changing flow, think about getting a second pump to run it. Notion is, if you change resistance in the overall return line, you will change flow to the tank, and those Herbie/beananimal type overflows absolutely rely on constant flow to the tank... Its not an end of the world sort of thing probably, but it can make them much more finicky to control. Some people do it with no issue tho... Other things with constant flow - fuge, frag tank, carefully designed algae scrubber, etc, SHOULD be fine. Some people say nothing but the display tank on the main pump though, and that would be the safest way....