Effect of Free Super Charging for Life to 2019 LR Model X

If you regularly charge the battery to 91% you will, eventually, get a warning message to the effect that you are going to shorten the battery life and at some point the BMS will step in and limit your charges. If you regularly charge to 90% you won't get any such messages or limitations imposed. This tells you that Tesla thinks that regular charging to over 90% is a bad idea and it is pretty well known that this is the case with lithium batteries. But how bad an idea is it? No one will be able to give you a hard number such as a statement that hard charging reduces the life life of your battery by 0.764%.

It also seems sensible to conclude that 90% isn't a hard limit and that charging regularly to 85% may extend your battery life relative to 90% charging, Again the question is as to how much improvement this might get you. Note also that the president of the company has said repeatedly that charging the car to 90% won't hurt it.

Add to this that your projected mileage of 5,200 mi/yr is well below the 13,000 mile average for the US and I think you will probably be OK with your plan but I certainly don't have any hard numbers for you.