Hmm, well ktspktsp banged the shit out of me last night for what seemed like ages
but it was probably 15 mins tops, in the end. You're right, I probably would get a bit sore/raw after longer than, say, 20 mins. However, I can handle oral for probably 30-45 mins (since there is less friction in the vagina, but more on the clit, which gets more sensitive).
Then again, I don't really keep a stopwatch on hand for these events...