This was also a very heavy load being used in skeet choked guns. As you remember, Dryke won the skeet gold in Los Angeles in '84. Certainly, those open chokes worked very well with high velocity loads. It is also very possible that high velocity was necessary to generate enough energy to break the harder International type clay targets. Standard American type clay targets are softer and break more easily.
Higher velocity means more initial shot setback and distortion.
Squashed pellets tend to wander out of the pattern. Has to be. Got to be. Then again, a heavy load of shot also causes increased setback due to crushing. I don't know where the pellet damage curves cross when you compare a fast, light load to a slower, heavier load.