one of most player's potential weaknesses is that once they get to a certain point in the game, they focus less on peon production and more on offensive units. but like i said, spb always focuses on peon production. so if he loses 20-30 peons, but quickly replaces them, and manages to dk the enemies gold peons, and the enemy isnt as proficient at replacing those peons.. spb is ahead... but spb does not have a conventional style.
Even though I think it would be very difficult to figure out the exact numbers, I think there's a point where setting up an expansion and the cost of a huge amount of peon production can take such a long time to break even on that its not necessarily worth it for awhile.
For example, even though I come from a bne/f background, and still prefer it, I've actually always been more of a micro-oriented player than macro. There are times when matches go to late-late game and I'll get outmined by 50-100k and still win, or lose when my opponent has less than 5k banked, and I think its largely due to making so many peons and the cost of expanding, something I don't do a lot of. Maybe the way I play will ultimately stop me from ever evolving to the next level, but most of the time I'm just fine with 1 or 2 halls mining gold during late game.