Don't forget track conditions.
At Road America in the early (colder) Spring, I was lucky to run 2:35. In the heat of the summer, I ran 2:28. That's 7 seconds on a track about 1/4th the size of the Nordshleife. And I ran "softs" in the Spring and "mediums" in the Summer.
At GIR (my times were about 3 seconds off in the colder Spring versus summer times), track about 1.6 miles.