1.2BTC to retire right now and live for 30 years? I suppose it depends on where you live, but I'm skeptical that this would be enough unless you're already self-sufficient. In most developed countries you'd likely spend that down to zero before the next cycle top. You need to have enough to last you through the beginning part of the growth curve and still have enough for future appreciation.

I tend to think this is going to be somewhere around the correct answer. Maybe a bit more than this, aim for 1.5BTC to be safe. Cost of living will go up over time but Bitcoin should outpace that.