EGR came about to lower combustion chamber temps to keep NOX levels at bay. It has been called the poor mans octane booster since it is inert gas that wont burn. As far as I have ever been taught in all my emission classes I took as a tech thats the main reason they use EGR which is to fight NOX levels. It was not used to stop spark knock and detonation even though it does help fight detonation. And I can tell you that in 1976 when I worked at a Ford dealer if the EGR vacum hose came off the EGR valve the eng would ping right away and when you installed the EGR hose back on the pinging would stop right away but thats because of how the engines were set to run with the EGR. And of course I cant see anyone with a performance car wanting an EGR system on it but I have seen some use it when they try to make the emission eng in their car a performance eng and run on low grade pump gas. The later year cat converter's were made as 3 way cats as they would control HC , CO and NOX as the first cats were called oxidizing cats and they only controlled HC & CO and used platinum or palladium in them. The later 3 way cats were called oxidizing and reducing cats as they added rhodium to the cat to help control NOX. I remember around 1992 some of the Mopar 3.3 engines stopped using the EGR because they used the 3 way cats and were said to have good enough emission controls to not need the EGR. But we had some coming into the dealer failing emission test in having to high of NOX readings. And many times we could not find any problems with them so Mopar told us to replace the cats as that was supposed to take care of the NOX. But with todays technology like quench and the combustion chamber designs of the modern aluminum heads and the right cam specs you can build a 10.5 comp performance eng to run on 91 pump and have no ping. Ron