I would definitely go 100D.
The cost difference is about $25,000 which isn't insignificant however consider the following:
1. The car will depreciate about 40% over the next 5 years so you're really only paying $10,000 for the upgrade
2. The car will go considerably further...and everyone who owns one of these would like more range. That's the longest range EV on earth right now. Lots of people take trips to weekend homes (cottages/lake houses/cabins/farm properties)...and they're usually about 150-250 kms away from the city they live in. Owning a 75D means you're DEFINITELY on the hook to charge at the destination or to supercharge on the way. Owning a 100D means you are most likely able to roundtrip it with no stops and that's pretty awesome.
3. The 100D is MUCH quicker. Guys will say the 75D is quick enough, but A6 3.0T owners say that to convince themselves they don't need/want an RS7 all the time, as do Mercedes E350 owners say the same thing vs. buying an E63. Running to 60 mph in mid to low 3 seconds is pretty outstanding and something that will put smiles on your face for years. It will also stun your passengers and that's pretty fun too. (this isn't accurate
@aslam "and 0.1 seconds faster 0-100 acceleration (probably not even noticeable to the average human"...we're talking about the difference between 0-60 mph of 4.2-4.3 seconds and 3.5-3.6 seconds. That's a massive difference because the power to produce that gap is also present all the time. When going from 50-80 mph the 100D will be significantly quicker).
I'll sum it up like this. I have never heard a 100D owner say 'Man I wish I'd saved the $10,000 and bought the slower, less exclusive, shorter range car'...however when I talk to 60D/70D/75D owners lots of people talk about how nice it would be to have a 90D/100D for a bit more range and comfort and less reliance on charging networks.
NOW...I could also make a very compelling argument for buying the 75D. There's tons of SC springing up so range isn't a big deal...and the rest of the industry is rapidly going electric so soon there will be hundreds or thousands of charging locations beyond just Tesla's Superchargers.
My history was I bought a 70D, then when the time came I traded it in for a P90D...so you can see where I would vote (and where I did vote).