Around 37 minutes for the (few) 3:00 marathoners I know.
But the second question is a tad different. Part of what makes 3 so big is it is a nice, round number that most people have to train pretty hard to achieve. I don't think the 10k quite has this. I think the closest is 40 minutes, but that is far easier to do than the 3 hour marathon. 35 minutes is just as round, but quite a bit more difficult. Perhaps on par with the 2:40-45 marathon.