Here are the Beyer pars for class levels at Belmont Park in 2006.
http://www1.drf.com/misc/drf_simo/tour/beyer_pars2.pdf
In less than six years time -- the pars have become slower at every single class level by 3-to-5 points on dirt and 1-to-3 points on turf.
Go back ten years -- and it's 4-to-6 points on dirt for virtually every class level.
Basically - a 100 Beyer today is worth a 104 six years ago - and a 105 ten years ago.
Thoro-Graph had a reverse of the same problem....instead of a shrinking scale -- they had a runaway scale.
However, in both instances, the pars have always stayed consistent on each version of speed figure.
Using todays pars, Secretariat would have been a low to mid 120's Beyer horse at absolute peak...and he still would be just about the fastest 3yo in history.