The 1st attempt in suede coated vibrams was a disaster.  The suede prevented chafing, but got pretty hard.  It might have been harder than the rubber, but either way, you're feeling nothing but bare concrete.  By mile 12, the paws felt like meatloaf.  Cramping in the calves soon followed.  It might have been several runs in 90F during preceeding days throwing the lion off, muscles being activated which weren't in shoes, or most of it being over 85F.  It was manely walking, after mile 14. Topped out at 18.4 miles.

Discovered cramping manely attacks if you stop moving.  Pacing around the apartment while drinking salt, potassium, & water got it under control.

Definitely need a minimal amount of cushioning to go beyond 12.  Taping the toes prevented toe plug chafing.  The orange farsteners became a real chafing problem & they never needed to be adjusted.  Replacing them with tape prevented chafing from those.  

The thought occurred of replacing insoles every few miles.  This would work in a loop race or using drop bags.  Very disappointing to have lost last year's fitness.