If you're really worried about the return pump being oversized you can add a pvc T with the "extra" end heading to the opposite end of the sump from the return. That end would have a ball valve so you could limit the flow to just bleed the extra off. This will reduce the head pressure on your return pump, and possibly extend its life. You can also use that end to make water changes easier if you're not sucking up detritus and you ball valve the end that goes to the return. Oh and most importantly you would have to use flexible pvc (HD and Lowe's both have it). That is how I have my return pump set up because I was a little worried about my pump being a little oversized, but it turned out fine. I usually use this method to do every other water change or if I am just in a hurry. I hope that its a little clearer than mud.