Such questions can be answered fairly definitively when more shooters start using Dr. Jones's pattern analysis program. Way too much of our pattern "knowledge" is based on an eyeball impression of one shot. Statistical "truths" are another kettle of fish.
I have compared a Hellis game gun that has a 7" choke taper of 0.035" constriction and an Ithaca 2 1/2" taper for 0.035" constriction. They both produce (drum roll) full choke patterns unless I toss a spreader wad into the load. I don't present this is irrufootable evidence of an all time and all place truth - rather as a pointer for the "normal envelope of taper lengths. I'd opine that extra long tapers would tend to more open performance than their constrictions would indicate and that excessively short tapers might well do the same. "How short and how long do tapers (large and small taper angles) have to be to produce patters divergent from expected for given constriction?" is a good question.
