In this context the two words are as good as interchangeable. Because "reasonable" is a value judgement just as "fair" is. There is no answer, as I said, it depends upon how likely you think a great outcome is (and how great that outcome will be). There is certainly plenty of room for reasonable disagreement here, you just have to decide whether you want a piece of the pie depending on how likely a positive scenario is.
Some people who think they understand Tesla could feel "reasonable" while valuing it at $250. Personally, I think I know more than they do and I don't find that "reasonable" at all. They do. So what? That's their right and they won't own the revenue stream as I will.
Some people wouldn't sell tomorrow at $5,000, I probably would. $250 to $5,000 is a twenty fold difference. What's reasonable? Only those willing to put real money on the line get a vote. Currently the "vote" stands at $1,627. It can and will go up or down from there. I know it sounds like I'm stating the obvious (and I am) but it needs to be said. There is no "reasonable" when the potential outcomes have such a wide range. Because no one can see the future. But those who are best at figuring out what the future looks like, end up with the most money.
I'm confident the more bullish TSLA investors will end up with more money than the more doubtful ones. Time will tell.