I've fished a good bit of saltwater with a 10wt (9 & 11, too) and have never had cramps in my hands or arms from casting - fighting fish, yes but not casting. Like I said, I think it's a function of what you're throwing - EP minnows, Deceivers, etc on a floating line weren't all that taxing, big Clousers, Half & Halfs on a Teeny T-450 are another story.

Regards,
Scott