First; if it were known for a certainty how many pellets are required to break a target, Larry Brown and Andrew Jones would have nothing to argue about.
For regular clay target shooting, nothing can have more retained energy than a #7.5 launched at 1330 fps. At 60 yds that equates to about 0.9 ft-lbs per pellet. I've seen enough targets smashed at 60 yards to know that such a shell is adequate. OTOH, I can say that, while loading teal machines on a course, I've stood under teal targets 60 yds from the shooters and heard pellets tinking off them.
Clearly, a single pellet strike at any distance can be insufficient to score a target dead. So, when using #7.5 @ 1300 fps and I have any doubts, more choke is the answer. One ounce of #7.5 @ 1300 fps and IM or Full accounts for every target I break beyond 50 yds....whether a FITASC target, second shot on a bunker bird, a hard angle 27yd ATA bird or a Bo Whoop Challenge pair.
IME, a load of #7.5 will break anything that's perfectly pointed at 70 yds. I no longer play any games with longer shots. But if I did....I might be tempted to use #6 if they were allowed. Started at the same velocity, a #6 will retain the same energy as #7.5 for an additional 10 yds. In other words, I trust the .74 ft-lbs of a #7.5 at 70 yds and a #6 will still have that at 80 yds. Then there's the diminishing return of pellet count and at some point luck becomes a big factor...the point where a perfectly centered bird is lost to a thin pattern.
All things considered, the best shooter will likely win out to 70 yds or so. Beyond that, luck plays a big enough role that most anybody can win.
At a Canadian FITASC shoot 20 years ago, The World's Greatest Target Setter (his articles say so)set a 90mm Midi target quartering away from a trap set a measured 90yds from the peg. One C class shooter broke it with a light mod choke. The Target Setter rode him around in his cart all day to validate the fairness of the target.
