Arthur, i've been by your place twice and if you plan on keeping the tank where your 125 is and using a sump, I would HIGHLY recommend the bean animal. I had a 100G setup about 5 feet from my couch and I didn't hear a thing from the overflow. (once tuned properly) The only noise I heard was from the return (internal) pump. It's a pretty simple concept that uses a siphon and has a backup for the "just in case" scenario.
I found the best way in my 100G was to put the overflow box in the Top-center of the tank so that the water movement wasn't coming in from only 1 side of the DT. The drilling is pretty simple if you have the right drill bit.. Took me about 20 minutes to drill the 3 holes (borrowed a bit from Reefwise). You"ll have to be patient and do not rush the bit - GO SLOW. Turn the tank with the side you want to drill facing up. Get some plumbers putty, make a large enough ring around the area you want to drill and fill it with water. Doesn't have to be deep, just wet. Make sure to place a towel on the INSIDE of the tank so when the glass (from the hole) falls through, it hits a padded area and not the other side of your tank. If you don't do this step you will almost certainly crack your tank, on the opposite of the where you're drilling. Do this 3 times and then hard part is over.
As for placement, it all depends on how big your overflow is. Mine in the 100g was about 18 inches long. it was a FULL box.. none of that 3 sided, having to weld onto the tank stuff. The reason I had FULL box was it didn't require me to glue or silicone a box in place. Instead, I cut 3 holes into the overflow box and simply used the bulkheads to keep it in place. From the inside out, it was in this order "feed the 3 bulk heads through the Overflow box; place the Bulk head O rings / gaskets / seals over the threads; then feed the bulk heads through the holes you drilled in the tank; tighten each nut onto each of the 3 bulk head threads. Now you'll have to build the actual plumbing.. YOu can find that information here:
BEAN ANIMAL'S OVERFLOW
So now that this has gotten long - recap: Bean Animal Overflow using an internal overflow box - Centered in your tank to provide the most water distribution / waste removal into the sump.
Good luck and sorry to hear you're shutting down the 125. it was a great looking tank!