So there's no way to give a general guess at what this situation would do to the pattern of any shotgun?
I don't own the shotgun mentioned, nor do I actually have those shells loaded. What I'm asking is basically the effect of velocity on pattern, all other things being equal.
We can all
guess, problem is no one can
predict what will happen in a given shotgun.
At least part of the problem is that "all other things being equal" is seldom true. In your example you changed
both the wad and powder, not just the velocity. To isolate the velocity variable, you'd need to use all the same components, just more powder. But, of course, doing that would also change the peak pressure. And while some would argue that peak chamber pressure should have "no" effect on patterning, that's wishful thinking without being able to prove it.
Bottom line; even if you managed to convince yourself there was a patterning difference in your tightly controlled test, odds are someone could produce data showing the exact opposite with other loads in another gun.
At the end of the day, what benefit is there to a "general rule?" Even if you thought you could say with 80% certainty that such and such will happen, is that good enough? If it's really important to know, it should be worth spending a few minutes patterning to find out for sure.