Hot Rod Magazine article on oil temperatures.
What Is The Optimum Engine Oil Temperature? - Hot Rod Magazine
"A quality conventional motor oil will tolerate oil sump temperatures of up to 250 degrees, but starts breaking down over 275 degrees." [...] "A full-synthetic oil will withstand sump temperatures in excess of 300 degrees, and for hard-core professional racing, some oval-track race teams are experimenting with ultra-thin, specially formulated, race-only synthetics operating at 350 degrees or even higher."