Just by the tone of your post, it's obvious that you long to move to something else. And frankly, you should.
The only math that I would do is a reasonable estimate of the future valuation of your unvested stock. Is it really significant enough to keep you there? The alternative is that you would start your own company as a co-founder, own millions of shares of something that may be worth nothing or a lot. How does that compare to your current situation?
Presumably, you should have enough vested that if your current company is the next Google and your next one is a flop, you still get a nice pile of cash.
Otherwise figure out for sure exactly how big the carrot is they are dangling. Everyone has a price. The beauty of stock options (from an employer perspective) is that the employees never really know what they are or could be worth. Additionally, if they got funding the VC's probably have all sorts of clauses where they get their money back + dividends + their preferred stock in a buyout, further diluting you.
Chances are the strike price for purchasing your options has gone up in the last 4 years.
Also, the investors might want to bail and get their money out, selling the company at a lower price than if they had waited. Or a competitor could come along and wipe out your growth, killing the potential value of the company.
Or nothing could happen. The company could make nice profit and just exist, seemingly forever, never selling. You'll wake up one day 5 years from now, no further to the fat bank account than you are now, and wonder what happened.
Many things can happen that are outside of your control to these stock options that are keeping you there. The only thing you really have control over is whether to stay or not.