Don't forget you have to maintain siphon in the overflow itself to prevent main tank flooding once return pump is turned on. Chuck Gadd has a nice explanation: http://www.csd.net/~cgadd/aqua/overflow.htm
Just thoughts, but hopefully someone with a much bigger tank than mine answers. I can see the appeal of overflows on opposite sides of the main tank, with the retun line from the sump in the middle, but don't think it will be any more effective than overflow on one side, return on the other, and powerheads in potentially dead spots to keep stuff suspended and headed towards the sump flow. Return line near the bottom of the tank would not only help with lower head height, but should be more effective kicking falling bits up than a power filter is sucking, since you're probably aiming for >600gph from the sump for your 125g.
But to answer what I do, I have 17.5x turnover in my main tank from the sump alone, and before adding a Durso standpipe on the bulkhead, had to turn off the return pump to keep flake from going in the drain. I happen to have a planted ground cover so don't take as much care with stuff on the substrate as, say, aquarists with sand and no plants. I just graze my substrate with a gravel vac every now and then. Most all the bad stuff ends up in the sump on its own.