If it's trivial to get there, then why wouldn't you be willing to go higher? Remember, you double your entire savings if you win. No matter how quickly your marginal utility curve flattens, it seems absurdly risk-averse to name any number lower than half of whatever you think you need in order to retire.

I'd need about two mil to retire comfortably I'd say. It's far easier to get to that from one million than it is to get to one million from $5,000. Hence I'd be seriously screwed, especially at that age, If I found myself with $950k and had to lose it all, whereas had I not made the bet, I'd probably be at most 5 years from retirement.

Two million to retire comfortably? That's quite a standard of living. Supposing you're earning 6% interest and expect to live to 100, that's a budget of $10725 per month. That's enough to spend the rest of your life living in the penthouse suite of a cruise ship.

Right. Exactly

A retirement on half as much income as you'd like seems a lot better than a retirement on $5000...