My first guitar was a spanish 12-string built to some zany bigger is better principle. With a nut that must have been over 2.25" wide and low-rider frets but a featherlight action, it simply took a lot of barre'ing. I don't remember any finger pain, just lots of frustration.

My old Yairi flamenco has a deep oval neck and classical width, never any pain there either. The jumbo frets and nylon strings, or maybe even the musical style may have some influence on the

The Ovation 12-string with (I'd guess) a medium deep "V" eventually seemed to cause some cramping when playing lots of barres, and I've essentially quit playing it.

The Takamine EN-32C has a medium oval neck, and wider than average nut (dunno the measure), and I've only noticed hand problems after several hours of practice.

And just to add to Vixen's comments: I've noticed the same thing about left hand cramping when playing low-D whistles. Its roughly the same muscles/joints that ache when playing guitar, mostly near the base of the left thumb. I suspect it has to do with how much time the left index finger spends stopping holes in comparison to the others, just as the barre chords do for guitarists. It definitely has something to do with repetitive stressing of the same tissues.

~S~