Like Kirk said, what type wood, mostly. A 50 HP 3 phase will require the sawyer to do the sawing, not just being a stick puller, like on some mills. White and Post Oak, along with Hickory will be the ones to watch. Not familiar with them Mass. logs, especially them froze up ones.
Only electric mill I ever saw running, used a 75 HP and it just sailed through Red Oak.
I'm sure Frank can handle things well with the 50 HP.