At 14 feet to the rafters, I'd just go full height and insulate the room well. I have a 24x40 entertainment room with a 15 foot ceiling in my barn. When I added the room I didn't notice much of an increase in propane use versus what I had been using. My ceiling is has fiberglass blown insulation at R40. I installed a vapor barrier and installed blown in fiberglass insulation in the side walls after my wall board was on. It was a little more work that way but I have about 8 inches of insulation in my sidewalls. My room has only two windows and no doors to the outside except for a walk in door going into the unheated part of the barn.
I'm assuming you're planning an overhead door from the unheated space going into your shop space. I'd go with an insulated door, insulate your ceiling and walls well and call it a day. I use a residential 92% efficient gas furnace in the entertainment room as well as in my 30x50 shop. I'd set the room up with one or two ceiling fans to move warm air down off the ceiling and install the heating system with the return down low by the floor and the heat coming out up high. Some might go with a 30% high/70% low return setup but I figure why add the cost for the small benefit you'd see.
If you'd like to bounce some ideas around, shoot me a PM and I'll send you my phone number... as long as you promise not to use it against me in the PARF
I have a background in residential building and HVAC. I might be able to give you a few pointers if you'd like.