I'm not so sure. Secretariat was awesome but something like 3 or 4 track records fell that day and his main competition more of less broke down in the race. (I think there was a post about this after Commendable won the Belmont) PG ran a helluva race, actually looked a lot like Secretariats and it sure would be something to have seen them lock up and that day. Even by your math, Secretariat wins by 15 and that ignores all the improvements in the breed, and everything else which has lead to faster horses in the last 30 years. Assuming equal groundloss etc. I'd give it to Secretariat by three give or take a length.