Thanks for the photos, you have some seriously nice machines.
I've only begun exploring servos myself so probably should have stayed out of this conversation. I'll offer some thoughts anyway. Power characteristics of steppers and servos are apples and oranges, think in terms of machining force. Servos are not typically run 1:1 and they don't need to be as their power doesn't fall off with speed as seen with steppers. 850 oz-in servos 3:1 would probably be gobs of power but a supplier could give some real world numbers. The bf46 comes cnc prepared with drop-in ball screws available if you choose to go that route. Most of us should be so lucky.
Wish I could be more help
Anyone who says "It only goes together one way" has no imagination.