Speed of sound is 1150 fps, at sea level, although I use 1135 fps when calculating anything.
If you will look at the lyman shotshell Reloading manual, and go to the tables, you quickly see that all that extra velocity is lost in the first 20 yards. Really! That was the big shock to me( too!).
1400 fps at the muzzle works well when shooting RB, or slugs, but Not with shot. No matter the size, a RB has such a poor Ballistics coefficient, that it simply cannot and will not retain that velocity ( over the speed of sound) for very long traveling in air.
The big problem with high velocity loads is what you discovered- that is-- it plays hob with your patterns, regardless of choke used. The bast choke tubes I have found for good long range patterns are those that extend beyond the muzzle of the barrel, with long tapers to the choke, to choke the shot slowly. These are the chokes sold for Turkey shooting, and for the Crow shooters. The shorter, muzzle flush choke tubes reduce the diameter of the barrel too quickly to give good patterns with the fast loads beyond 45 yards. Briley has experimented with long chokes, and with back boring, and even with shallow straight rifling, to keep the shot cups from turning in the barrel, and giving a slow "spin" to the shot charge, all to improve shot pattern density for longer range shooting. Straight rifling was done more than 40 years ago by Perozzi and found to deliver 96% or better patterns at 40 yards. More recently, a friend of mine fired patterns with the newest "Olympic load", that is 24 grams of shot and 3 1/2 drams equ. of smokeless powder. The light shot charge gave the load high velocity(I don't recall the velocity off hand), and he noticed that he didn't have to lead the clay targets at all to break them. He got 98% patterns with his Remington Model 1100. He concluded that the shot just got to the paper so fast it didn't have time to spread out further. He attributed that solely to the small weight of the shot charge, and not to the plated shot used in the loads, or to the special long throat choke barrel he had on his gun. I saw his pattern papers and they ranged from about 93% to a couple that scored 98%- so it was no fluke.