I think your goal is reached. And then some. My room is about three times the size of yours (if not more) and I can play it at reference with "only" two Ultras.I have not tried WOTW with all 4 running yet but I think it is about time to try. My goal is to be able to play this safely at near reference volume. Good for you for making the right decision. Enjoy!
-Robb