My last race h  7ff9  ad three corrals, and the amount of walkers in the first corral that was supposed to be for under 9:00/mile runners was ridiculous. I spent the entire first half mile weaving through slow people, then consistently passed hordes of people for the rest of the race and I was averaging around 8:20/mile. I wonder if you'd be justified to just plow through them since clearly they're not where they're meant to be. I have so much respect for actual ulta-runners, I can't imagine running a race with them, I'd be too blinded by their awesomness.