For those that don't know what a Livingston is, it's a catamaran hull that needs a good deal power to get much speed. I have two of them, fairly stable, and for the size there's a good deal of room. I have an 8' that I've been three miles out in the Pacific off the West Coast of Vancouver Island in BC Canada with two people, and it wasn't bad at all. I could throw it the back of a small pickup by myself and fish many different bodies of water.
I have not tried my 14 ft Alumacraft 1436 LT jon with two people yet, but with my Evinrude 6 hp and just me my fishing gear,3 gallon fuel tank full, Optima marine battery, 45 lb Minn Kota foot controlled trolling motor mounted on the bow, I have so far GPS 16.1 mph max. I'm 6 ft 190-195 lbs so I'm assuming someone else aboard roughly my size will knock the mph down considerably.Go for a 9.9. Will get in you some lakes with HP restrictions. Your key words were "2" guys. I had a 7 ? on a 10' Lowe "Lake" John and it did ok with just me.