100D seems a lot more money for not much more and the base’s range seems enough.
Its hard to justify the money on range-difference alone, but the Sums should not be done on "I'm paying £X more for additional Y-miles range".
If the 75 will do the majority of your journeys, even in bad weather, then stop there.
If you do longer journeys then you need to factor in recharging time. All the cars charge from 10% to 70-80% in the same time. Of course with a bigger battery you get more range for the same percentage. If a 100 can get you to destination, without charging, the saving becomes worthwhile (if you do that often enough ...).. To charge you need to include the time driving off the road into service station, hook up, unhook, return to the road, so even a 1 minute splash-and-dash is going to add 5 more minutes to the journey.
You need to allow, say, a 20 mile buffer for detours / whatever. This is obviously a larger proportion in a smaller-battery car, so your "usable range" is proportionately less.
I've used A Better Route Planner to compile some comparison figures (below)
The other thing to factor in is how much you might save on Electricity vs. Petrol. If you can charge at work then that's free (no Benefit-in-Kind tax on that). if you use your home electricity then my sums suggest it saves about £100 per month for each 10,000 miles you drive a year, At 16 mile commute I guess you don't do much, but for a high-mileage driver its a fair chunk that you can put into the Finance each month to even-up the books.
Worth considering Economy-7 electricity tariff.
Service costs have been quite high for Tesla MS / MX - given there is very little that needs doing. I service once a year (about 27K miles p.a.) as there is no need for regular interval servicing as with ICE.
Also, much less wear-and-tear issues. I used to change ICE at 3 years, 70K miles, in order to avoid maintenance problems thereafter - that would not be a concern for EV. However, with the advance of Tech there might still be reasons to change ... although Tesla OTA updates have bought me a decent handful of new features and improvements.
more range lets you drive at faster speeds to go the same distance since higher speeds reduce range
Well ... "it depends"
If going on a road trip where you are going to repeatedly charge-drive-repeat then there is an optimum speed where driving faster saves more/as-much time as charging. Driving slower gets you further, takes longer, but you charge less. That depends on perfectly spaced Superchargers ... which are likely to exist in USA but certainly not in UK where chargers are likely to be "only one choice for the journey" and thus odds are a bit long that they will be ideal ...
A Better Route Planner posted some graphs of optimum speed vs. charging speed, and optimum speed is as high as 100 MPH for some models.
But if you are going from A-B with no charging, and borderline range, or you can get there with only one charging stop, then optimising for range is likely to be quicker than max speed.
Cold weather or torrential rain is more likely to sap range here in UK
In UK I find that a stretch of 50 MPH for Traffic or Roadworks, on the motorway, reverts a lead-foot back to average consumption
once you are on the final leg, i.e. can reach destination, then you can vary speed to arrive with appropriate charge level (there is a dashboard display of graph of energy-use for remainder of journey, so easy to see what your predicted arrival-charge% will be and slow-down / speed-up accordingly)
Here are the figures from the tests I made. I have gone with the Wh/mile, for each model, which A Better Route Planner gave me (ABRP has published figures of the averages that have been achieved for the fleet which uses that APP, so I presume they are "reasonable", at least for comparison purposes.) I picked a cold winters day (a couple of degrees above freezing, 10 MPH wind)
My test journey is London to York which is borderline distance for the longest range model in the fleet. Even for the shortest-range model it is still only one recharging stop. If you routinely drive Lands End to John O'Groats!! I recommend that you test that particular journey to see what the difference for multiple-journey-charging-stops is between the models.
Note that I have used an arrival-charge of 10%, but in practice for smaller batteries you will probably want to allow more (representing, say, 20 miles), and that will increase charging time somewhat.
ABRP plans this journey as:
Start at 100% charge and go via A1
4C, 10 MPH wind
115 miles to Grantham Supercharger
88 miles to York, arrive @ 10% charge
203 miles total
There is a more direct route, but Supercharger not well spaced:
M1 208 miles Driving time 3h13m @ 70MPH, 2h55m @ 85MPH
I made tests with these variations to settings:
a) Max speed 85 MPH, reference speed 110%, driving time 3h6m
b) Max speed 70 MPH, reference speed 100%, driving time 3h24m
MX 75D (324 Wh/mile @ 65 mph)
a) 31 minutes charge 14% - 79%, Range 131
b) 24 minutes charge 21% - 73%, Range 139 - i.e. Driving +18m charging -7m, net +11m
c) as (b) but "Summer" - 20C, 5MPH Wind, 16 minutes charge 29% - 66%, Range 148
MX 100D (386 Wh/mile @ 65 mph)
a) 12 minutes charge 36% - 61%, Range 156
b) 7 minutes charge 41% - 56%, Range 162
c) 1 minutes charge 48% - 51%, Range 170
So could do the (c) journey via M1 arrive at 2%
save 11 mins driving time.
So IF you make this type of journey often enough, the 100 is going to save you 10-15 minutes recharging time each trip. For me that's quite significant. If you are happy to sit there and do Emails, which you won't then have to do when you get home, it may be as broad as it is long ...
... if you have to charge on the way to a meeting, then you have to leave 15 minutes earlier ... but you've still done some EMails
Also if you have a regular journey longer than 130 miles, but shorter than 150 miles, you will completely save the recharging stop.
Of course this is even more important if your (repeated, regular) journey does not have a Supercharger at a convenient point on the journey.
For comparisons here are the other bottom/top-end models:
MS 75D (386 Wh/mile @ 65 mph)
a) 15 minutes charge 30% - 65%, Range 150
b) 12 minutes charge 34% - 62%, Range 154
MS 100D (386 Wh/mile @ 65 mph)
a) 1 minute charge 48% - 51%, Range 170
(clearly could just choose to arrive a bit less than 10% instead ...)
The M1 route would have no recharge, arrive @ 10%, 208 miles, saving 11 mins driving time = 3h13m
M3 LR (286 Wh/mile @ 65 mph)
a) 12 minutes charge 37% - 61%, Range 157
b) 7 minutes charge 42% - 56%, Range 163
M3 LR Aero Wheels (247 Wh/mile @ 65 mph)
a) 3 minutes charge 45% - 54%, Range 167
b) 1 minutes charge 50% - 54%, Range 173
Can route via M1, 208 miles, arrive at 6%, driving time 3h13m
M3 SR (247 Wh/mile @ 65 mph)
a) 26 minutes charge 19% - 75%, Range 136
b) 22 minutes charge 25% - 74%, Range 144
