Does a specific degree of choke say .040 equal the same performance for all gauges, cartridge types, etc ?
Obviously no as the variables between cartridges and bores are significant as well.
Does the constriction of choke have value and meaning?
Undoubtedly yes.
That said the only way to know how a specific barrel constriction performs with a particular cartridge loading is to pattern your gun and conduct an analysis of the a number of patterns (say 5-8 test patterns)
The reality is most of us have patterned a load on a couple of targets, but most of us have not repeatedly tested a number of loads and conducted disciplined analysis because it is a pain.
I have in the past tested loads, but never to the highly disciplined degree required to provide give near unimpeachable and reliably solid answers.
One comment on 40 points of constriction in 12 gauge vs 40 points in smaller gauges. I believe you must think of constriction in terms of a percentage reduction in size of the bore. This is why 40 points in a 16 ga provides greater relative choking than it does in 12 ga. Because the effect is linked to a percentage of reduction 40 points in a over-bored 12 ga say .740 bore vs 40 points in a 13 bored (.710) 12 ga is a much greater percentage reduction in bore and therefore
Reference Geo's comment on cylinder, I find little to no choke works if you engage targets rapidly when they are close, but as I get older and slower more choke is better and for distant shooting it goes without saying. On preserve birds I often shoot cylinder in the first barrel as I get close shots(sub 15 yards)
