OP has requested that the Model 3 perform absoutely in the worst case scenario. Must be able to go up to 300 miles, not need to stop ever at a Supercharger that is full, doing this in sub freezing temperatures. Being able to run at higher speeds and not stop to charge when it is prudent to do so.
Perhaps this is an unrealistic expectation and might result in an unsatisfactory ownership experience.
The best experience in any EV is to understand where it is great and not so great.
For the time being, an ICE vehicle with a large fuel tank, will still be best for non stop high speed runs.
I used to be that guy, and cherished my Grand Cherokee with 25 gallon fuel tank. It could go 500 miles without needing fuel. I prided myself in driving "straight through" but often arrived exhausted and miserable all the next day.
Since getting my X a couple years ago, I am a changed person. Now on long road trips I leave a little early, drive for 3 hours or so and stop for a late breakfast while I grab a charge. Get back on the road for another 3 hours and stop for a bathroom break to get rid of my breakfast coffee and walk around a bit to check out the area around the Supercharger. Then another 3 hours and plug in for the night. Get up in the morning and repeat.
My life is much better. My attitude is to enjoy the trip instead of just suffering through a long trudge.
It is something that is hard to imagine, or describe, but the travel experience is far better. I never get frustrated hunting around for the cheapest gas station, eating in horrible gas station mini-markets, standing outside pumping gas or dealing with payment of all that gas I was burning.
To re examine the original posts it is kind of like asking if someone should buy an Audi over the Camry they are currently driving. Asking if someone would guarantee that the Audi would be as reliable as the Toyota, if the Audi could run on regular gas as the Camry uses and if it would be as comfortable riding as the Camry. The question itself is a bit self defeating. I remember Elon answering a question as to how a Tesla would loose efficiency in 20 degrees below zero. He commented that the ICE vehicle probably would not even start in those conditions
The Model 3 is fast, comfortable, great looking, offers a fantastic driving experience, is proving reliable, safe and makes a step of getting weaned off burning gasoline to get around. Focusing only on range, in difficult circumances rarely encountered is missing the point a bit.
Did I mention the Autopilot is fantastic and getting better...