A double is typically hung on a 36" haft. I wouldn't go any shorter than 32".
But deciding handle length depends on the axe's intended use. They were originally marketed as felling axes. The 36" haft gave them both more power and more reach. In old timey logging photos you will often see them with 40", 42" or even up to 48" lengths.
For splitting work I still like the 36" haft for its added power. For bucking the haft length will depend on your own stature and the size of material being bucked. Also depends on whether you're bucking from atop the log (fastest but not always safe) or from the ground. Atop the log with a short of haft you're bent over further causing poor balance and constricting the diaphragm making it harder to breath. This gets worse the larger the log you're standing on.
Trail work or clearing is a lot different than bucking in a logging competition. Frequently it will be unsafe to stand atop the log.
I'm 6' tall and prefer a 32" to 34" haft for bucking. I'm typically bucking a log 8"-16" in diameter. For logs greater than 16" I'll try to cut them with a saw. If you're going to buck a large (24" or greater) log from atop than you'd like a longer haft, probably a 36".