Hello Richard et al.
typically stress engineers using Kellogg method as the first level of screening since it is a conservative approach (and at the same time incomprehensive one but quick).
in fact, the whole philosophy behind this approach is its conservativeness.
as an example for an 8"#150, we know that it is almost impossible to meet the minimum required gasket seating stress if your gasket is a spiral wound (10000 psi), while in the new UG-44 this flange has the highest moment factor (1.2).
new changes make this approach neither more comprehensive nor more conservative, and in my opinion it cannot be used with a peace of mind.