Been in several ...
I've been in a few, probably a half-dozen. I'm no experienced contestant, but I've taken on a few people that claimed to have won several in college or in other places.
And I slaughtered them, utterly. Typically twice as fast as any experienced eater and several times over anyone who is casual.
In several cases it was so out of proportion that they started loading up my plate with their stuff, reducing their load and increasing mine, and I still won.
Of course, I've thrown up afterwards in every case. I've always just stomached it as it's happening, but once it's over, I head to the bathroom and let it all go.
I guess that's why I've never had a gag problem eating a woman out (man I've cut through serious bush in my time!). Nothing going into my mouth ever bothers me. It's only when it takes out my stomach that it will actually cause an issue.