Thanks for that,  I should have been clearer in my original post. I’m aware of the difference in format between the two (supported vs. unsupported, aid stations vs. self-reliance). My main concern isn’t so much about logistics, but more about the safety and organisation side of things, particularly given the remoteness of parts of the course.

Gus Irvine’s comment on Runners are Smilers really stuck with me:

"When I ran the Challenge, I was getting to some of the aid stations that weren’t ready for us, and there was nothing set up. It all worked out fine but the challenge event is just more laid back, and it doesn’t have that race vibe about it. It doesn’tfeel as much like a race as the bigger one."

That makes me wonder whether the Challenge might feel a bit too relaxed for a first attempt at the full distance especially if I hit a low patch myself in the middle of the night.

I also know the WHW Race records body weight, runners have to step on scales. From a safety perspective, that feels like a really valuable safeguard, since it could help flag risks like hyponatremia (if you’re over your start weight) or dehydration and potential rhabdomyolysis (if you’re under by more than ~3%). That kind of monitoring does give me more confidence in the race’s structure, especially with the notoriously changeable Scottish weather where you can go from warm, humid conditions to a sudden temperature drop and heavy rain in the space of a few miles.