I have found if you have a tight choke relieved you end up with a much longer parallel than normal for a more open choke.
In one particular gun this still gave me around half choke patterns in spite of the 10 thou constriction.
However it only took another few thou to give me Improved cylinder patterns.
Another gun I tested recently has 14 thou constriction but gives nice IC patterns.
This particular gun has been taken out to .739 in the bore and has rather a long cone into the choke.
I too have given up on trying to guess with old guns based on constriction ,patterning is vital.
Although as you say it does give you some sort of baseline.
If I'm short on time I have found patterns measured at 10 yards are pretty indicative of 40 yard results.
