For what it may be worth, I did a gravel metric on New Year's Day. For some reason, I thought my fixed-gear '88 Diamondback with studded winter tires would be a good choice. To add insult to injury, there was a stiff wind that day, often gusting up to 50MPH.

So it was quite the grind, and I'd like to think I did the equivalent of 100 paved miles with a normal bike.
Here's a shot of our group (and my bike), taking a break. Man, we were dead by the end.
Here's more evidence. As usual, I was caught in an awkward pose (stretching my hamstrings, if you're curious.)

The blog caption reads:
Scott on his fixie commuter with steel rims, studded tires and single water bottle. Guess who wins the award for most overconfident cyclist? He finished though, which is pretty badass.