There are a few data points missing from this analysis: like over what timeframe the 5x returns were realized:

I can get that over 20 years with an 8% return!

Most VC funds have a 10 year lifetime, so all investment returns are for some period less than that.

Very good point, but it seems more likely that poorly performing companies have a rather short (several years) lifetime.

It's rare to get this kind of info out of a VC. I'm impressed with Fred's openness.

How will the YC model compare?

I'd guess a higher percentage of failures and higher average return on the successful companies. (It's a lot easier to get 50X when you only invest $15K to start with!)

From what PG has said (can't find the thread), most of the companies are still intact and the success rate is much higher than the average for VCs.

Yeah, that could be right. Of course, "intact" doesn't mean that they will have a profitable exit.