I didn't get anything like that after my 600k last year (or any of my doubles in the time before that), but after my 400k and at least one of my doubles this year I remember having some toe numbness "issues". I've had hot foot this year, too, which I'd never had before.

How are your shoes? Any changes in the last year or so? Swelling may have something to do with it for sure, but I'm also starting to wonder if a carbon sole shoe is the best idea for ultra endurance events. I switched from regular plastic-y soled road shoes to a carbon soled shoe before this season. The fit seems fine and is very adjustable, but I wonder if for an ultra endurance event your feet want a little more forgiveness than the carbon soles offer. Just a theory. For my next double I'll be using my old shoes just to see.