My knowledge about the role of tetraethyl lead in AVgas is limited to basically Wikipedia. But overall octane driver for both sides was feedstock quality (oil or paraffins).
The Wikipedia primary source that shows the Germans also had TEL production is given as this book:
Courtesy follow-up after some more digging. If you Google for "Technical Report 145-45" you'll find a PDF with the US report on German fuels that clearly indicates their use of TEL, and at what concentration.
The other major take away from that is the lean/rich Octane equivalents of the C-3 fuel were like 90/130 by wars end. So pretty good rich performance, but laggard lean, which would of course impact engine consumption rates in the larger DB 605.
The allies had widely available 100/130, and some 130/150 AVgas in the Pacific best as I have been able to find.
It comes back to the limited quality of hydroforming then mixed with synthetics for the Germans, vs FCC for allies. US crude wasn't of great starting quality, but they were better able to refine it at scale.
I believe the US late war high octane avgas was 115/145. 100/130 was indeed widely available more or less the entire war.
I think the British had something they called "150 octane", but I'm not sure that really was "better" or even different than the US 115/145, or was it different testing protocols etc.
Interesting, especially the 115/145. The octane equivalent #s from that era seem to be all over the map.
If actually 115/145, that's a big delta in performance for lean operation, and certainly helps the narrative. Do you have a primary source? I'd like to read further.
Regardless, what's certain is the Germans were in the high 40s mmHg for manifold pressure in late variant DB 605, vs the Allies were in the 60s mmHg for Merlins.
The Wikipedia primary source that shows the Germans also had TEL production is given as this book:
https://books.google.com/books?id=FDNyGpCS9WsC&pg=PA470&lpg=...