One of many guides on the net.
Transmission temperature/failure chart.
Note that, to some extent, you can deal with occasional higher transmission fluid temperatures with more frequent fluid changes. Knowing how high the temp goes, and for how long, will give you an idea of how frequently to change the fluid. Any amount of time over 250-260 and I would be looking to change the fluid ASAP and looking to avoid a repeat. Staying under 200 makes me happy. Staying under 180 makes me even happier.