From everything I’ve read, Peter Green was just as crazy as Syd Barrett.
Peter Green was not as crazy as Syd Barret. Green went nuts, but for the past twenty-thirty years had been sufficiently functional to play guitar with other people, and do interviews. On the Crazy scale I’d have put him about halfway between Barret and Brian Wilson of the Beach Boys, who is today reasonably sane and reasonably functional.
Danny Kirwan and Jeremy Spencer (both are also deceased, if memory serves), the other two thirds of FM's three guitar attack, lost their marbles earlier on. Gosh, I wonder if it was related to substance abuse? :^) Since Chris Welch died a while back, all four of the famous original guitarists for FM are gone.
Wrecking Crew musician Jim Gordon lost his marbles and killed his mother. He is still locked up.