According to "The Mysteries of Shotgun Patterns" by Oberfell and Thompson, their best estimates of the effectiveness of choke are the following:
They continue, "It is interesting to note two unique properties of the table; (1) within normal hunting range, 20 to 50 yards, an increase of 5 yards decreases efficiency by approximately 10 percentage points for the same choke, and (2) an increase of 5 yards requires changing to the next higher choke to prevent a loss in pattern efficiency. Thus, a rule of thumb based on the above data will make it easy for the shooter to make ready comparisons of pattern efficiencies at various practical distances. The rule is:
"Allow an increase or decrease of 10 percentage points for a corresponding decrease or increase of each 5 yards." Here is the table for this rule:
Now for my personal opinion (and only mine)--I have observed that by far the majority of my shots fall no farther than 25 or 30 yards maximum and I'd say a good mean avierage would be closer to 20. And that is on all upland birds. Of course there are the infrequent opportunities over that but I'd much rather be prepared for 90% of the shots than the rare 10%. Overhead shots are really interesting. A bird 30 yards overhead (90 feet) appears to be a distant speck and often a shooter hesitates to attempt it while gleefully blasting away if the bird is the same distance on a horizontal plane. It's an optical illusion, same as the moon appearing to be much larger when rising than when overhead. The same illusion applies to perceived lead. A 30 yard overhead shot might appear to need a lead of at least a boxcar length while a horizontal bird same distance might appear to only need about six feet. I think the reason for this is our binocular vision which allows us to quickly and accurately judge distances requires other fixed objects in our vision. Overhead objects lack this and we only have the single bird in view and our vision becomes for all practical purposes monocular, lacking depth perception.
Using the above tables an argument could be made that supports the use of a tight choke for all shooting conditions since a killing pattern could be delivered over a much longer range of distances. I have known some exceptional shots who use full on skeet very successfully. I am not one of those. My shot placement is not nearly as precise as theirs and I lack the coordination to perform to their level. Much of my shooting is in a much less formal field setting where the birds are rising unexpectantly, at random distances, and flying at trying angles often with all sorts of obstacles interfering. And often time does not allow me to untangle myself and take a proper stance. So my shots seldom center the bird and I need all the help I can get from a more open choke to bag my bird.
Interesting discussion.
