The 125 doesn't have to accommodate the extra water, the wet dry does, unless you're doing a dump filter (over the tank) and not a sump?I run my 125 a couple inches shallow that should be enough room to accommodate the water from a wet/dry filter right ? Tank already has a fx6 and large sponge but i tend to over filter things
Can also use aqualifters continuously running up into the U Tube(s) with airline tubing in order to keep air bubbles from forming. I agree though, HOB overflows are a nightmare from my experience. So much so that I traded a sump for a couple crappy canister filters (although I do slightly regret that, now that I have a tank drilled with a corner overflow)Honestly, I would never, ever, ever run a tank with a hang on overflow box. They're way more trouble than they're worth. Overtime, bubbles accumulate in the U tube, and unless you're good about purging them, you'll get reduced flow and all sorts of problems. They're incredibly noisy, they're unreliable, and they're not particularly efficient. You'd be far better off drilling the tank.
The big fear with a hang on overflow isn't usually that the power will fail and the sump will flood -- we know how to deal with that. Syphon breaks in the return, plenty of head room in the sump. The problem is that the U tube can fail, and you then pump the sump into the tank with no syphon down, and it overflows the tank. Been there, done that.
There's a couple of ways to go around this. You can put the pump on a float switch which will turn it off if the level in the tank gets too high, or if the level in the overflow box gets too low (depending on which type of float switch you get). You should throw out the single giant U tube that they give you, and replace it with 2-3 U tubes, and religiously purge them of air. A redundant one ensures that if something clogs it, you'll have less of a problem. (You can also add a second overflow box). Beyond that, its just a regular, religious check of the U tube for any obstruction, and removal of air bubbles. And living with the fact that it may eventually fail.
I'm also interested in this question. If I bought a tank with corner overflows then I wouldn't hesitate to use them for my sump (if I could pull off Herbie or BeAn Animal). If I were to drill/plumb a new tank, though, I'd go with something more "modern" like one of these --> https://aquarium.bulkreefsupply.com/reefing/Bean-Animal-OverflowMay I ask why?