FWIW, Honda crank bolts are often the "test" for air impacts...only the best 1/2" models can pull it off, and only with a proper supply setup - 100+ psi, inline oiler and big capacity to maximize CFM. Also, "cheap" 3/4" models will often perform weaker than the more modern, potent 1/2" models.
I've got an older CP 3/4" that used to see alot of use on International 4300 trucks - removing the lugs w/out at least a 3/4" impact are impossible. I remember watching a 320 lb lunk of tow trainee bounce on a 3/4" bar w/ a 6'+ "torque multiplier", aka leverage bar, attached and the lugs wouldn't budge - this after coming back from the tire shop w/ a bubble in one of the brand new tires. Anyway, now that it's gotten some age, it has to be warmed and patience is required for those same lugs, and now it sees use on tractor blades and suspension components. It's extremely heavy for constant use at anything other than a comfortable 90 degree angle, especially after shattering my hand/wrist a few years back, so I'm mulling an MG725 or equivalent for similar performance.
Anyway, to sum it up, for a "weekend warrior" with money to burn, I guess you can find uses for a 3/4", but for a pro with kids/wife/mortgage/etc, I'll have to justify an upgrade to my pile of CP. Or at least come up with bigger stuff to fix for a living.