Second-year colony boiling over — go vertical with another deep, or split her?

My overwintered colony here in Vermont has become a monster: double deep, both packed, bees hanging off every frame, three mediums on and they're drawing and filling the third already. No swarm cells yet as of yesterday, but the brood nest is getting squeezed by nectar and I know where that story goes. Second year, so this is my first time managing a truly STRONG colony and I see two roads. Vertical: more room — another super, maybe open the brood nest with a couple of drawn frames, ride the flow, maximum honey. Horizontal: pull a split now, bank a queen or let them raise one, guaranteed swarm relief and a second colony going into winter. I only wanted to run two hives... but I also really want the honey. What tips your decision — calendar, colony, or goals?