I use 3" to save my shoulder.
Look up the recoil table compiled by Chuck Hawks - the force (in ft/lbs) for a 10 ga is almost equivalent to dangerous big game loads used for elephants; the force from a 3.5 shell in 12 ga is similar. I've harvested birds at almost 60 yds with 3" 6-shot, I don't want or need to go further...
My 10yo son is shooting 3" from his Weatherby 20 ga.
I use Winchester shells, son will be using Hevishot Magnum 4,6,7 blend this spring. I'll be trying the Hevishot from a new choke before hitting the woods.