Nick,
most men (maybe women)are more comfortable singing in F or D (Martin's wisdom, choir background) it's all about blend of voices and half a note makes a big difference, we start in one key and notch it up til we find the one that works the best, hence I sing "Let the Toast Pass" in C at the top of my range cos it suits all our voices better (not mine, it is a bit of a strain), I sing "Spanish Ladies" in D at the lower end of my range for the same reasons, ron tends to use more obscure keys like F# and Eb to mention but two. The real difficulty I have singing with instruments is that for thirty years I have been singing in "Free time" and require instruments to follow me, acompanyists are a dying breed. Hot news though, we have been rehearsing with Damien Fynes and Frank Pallister and will be singing with instruments at the Black Swan Folk Club, 20th of July