From my research and talk with Tesla folks and Electricians, 14-50 is more than ample for 75D. 100D is where you'll see the best bang for that Wall Charger, besides the look. I'm in the same boat, leaning towards 14-50, largely due to cost honestly. Wiring was quoted extra $100-$125 + $500 for the charger, so makes a difference of ~ $600 for me. What did you decide @Antfugue ?
I'm still waiting for my referral to take delivery (we all know how long that takes!) In the meantime I've netted out the responses here that for my (takes breath) 6 gauge wire/40 amp breaker/S75 with 48 amp charger/85 mile round trip commute/can charge overnight/don't want to burn down the house/no one sees the inside of my garage situation It does not matter what I do.
So I guess I'll sell it to someone with a cool garage.