I've seen a lot of discussion where the consensus falls into the "clipless pedals are way superior to anything else performance-wise" category, yet 99.999% of what I've seen is based exclusively on the commentator's FEELING of what's better and what's not, and by what magnitude.

Because I'm debating using clipped/strapped pedals for randonneuring purposes, I'd like something much more numerical. I don't know where it was anymore, but I saw somewhere that the figure of a 15% improvement (of what exactly, I don't know) stood between clipless pedals (what kind? I don't know) and some undefined baseline. I can imagine a manufacturer trying hard to stack the deck in such a test, then facing little criticism because, hey, clipless HAS to be worth all the extra expense/bother/maintenance/clomping-around/etc. right?

I hear all kinds of things both ways when I look this issue up and I'd like some harder data if they exist.

In case you're wondering, right now I have a pair of Velo Orange's touring pedals with Christophe straps; if needs be I have some Shimano XP SPDs standing by and two pairs of shoes--an ancient but set of Nike shoes and a brand new (got 'em cheap) set of Time SPD hiking boots.

Any intelligent argument that doesn't involve subjective "feeling" one way or the other is hereby solicited.