I was just thinking about having that decision earlier in my career, before the dotcom bust. I had enough, but still had a lot in unvested options. I can't recall the figure, but I"ll bet it would've increased my worth another 25-35%. Seemed like easy money, and the kind of money I'd never get another shot it (partly because I wasn't going to take on another heads down, working crazy hours start-up job again) and it seemed foolish to walk away.
The bubble burst, making my unvested options worthless, along with a lot of my vested options that I hadn't yet exercised. It was another 10 years before I could ER. But I'm not sure what would've happened had I cashed out. I'd like to think that I would've diversified and rode out the bust fine, but I might've stuck it back in tech stocks, losing a lot of money AND being without a job. When I finally did ER I had learned and was much better diversified.
Anyway, stock options can be a very real test of what you'll walk away from, and what you won't.