I always find myself thinking similar thoughts, so here's how I'd go about it. First (and I'm very guilty of this as well) this is not a logical decision you're making, but an emotional one, so logic (like pro/con lists, numbers) are good but not that helpful. We already know the practical, logical answer: stick it out for a little while longer because you're not in a bad situation. You can achieve FI and then move to this country in a couple of years.
But on the other hand there's this "If I die while at my safe current job, was my life worth living?" It seems like your answer is no! If you were FIRE today, what would you do? Sounds like move to this other country.
Now here's the good news: you've already saved $300k at a relatively young age. If you earn only 5% on that for the next 15 years and contribute nothing you'll have over $600k and still be only ~50 years old. Play with those numbers and you'll see although you might be pushing FIRE out, you're likely not excluding it.
I can't speak to your Current job/location list, but having been in a similar situation in the past these are my ideas on the Prospective job/location:
Pros:
-Will develop and use many of my other talents [for a little while, until you learn the new skills and are bored again]
-Is in the location I have wanted to live in for many years [visiting and living are completely different experiences. for brevity: cultural differences, alienation, communication w/ friends/family, even daily things like going to the store change]
-Provides working visa, which is non-trivial
-Working with a team of people that I like [how do you know?]
-Has greater upside since company is small and growing [and greater downside]
-Even if it doesn't work out, would free me from mental chains I have to this job, could give me the push to start my own company [start your own company now or later, it's all the same. there's never a good time or a magical "push"]
-Would provide great experience on resume that could lead to a job with a comparable salary in the US [you already have a good job in the US]
-I already have enough assets to almost get by without working in the new location using 4% rule (about a $200/mo deficit) [seems like a good opportunity to test living in this country at no cost]
Cons:
-I won't be able to save practically any money for the first couple years [as I said above, stache will keep growing]
-Much less job security, especially if another economic crisis is coming [how likely is it that you can't find a job (any job) back in US? depends on industry]
-Going back to current position will be difficult, would have to pay dues again [always the cost of leaving. willing to pay it for this opportunity?]
-I might find things about the new company/location that I dislike just as much [you will]
-I will have less autonomy and be more dependent on other people for my work
-The location has some developing country problems [yet you still want to move there, so it can't be that bad]
-If something happens i.e. family or disaster/war in new country and I have to go back in a few years I will be still struggling for FI at the same time I want to be starting a family [lol @ "struggling for FI", at least you aren't struggling to eat! Families cost money either way: If you want to be FI before family then you need to stay put]
-The salary may require me to take on a room-mate depending on other expenses [does this matter if you're going after your dream job?]
-Moving and selling things [it's nice to eliminate all the stuff you think you need and reset every once in a while]