When I first started reading your criteria I thought you must be trying to describe "Immortality" for some reason. But then I got to the "white version of I. pallida" part and decided probably not. Anyway, I'm not sure that any of my irises are as vigorous, and not many are more fragrant. It can be really pretty, but whites aren't my favorites, so I have a hard time getting thrilled about it. And it's sort of lacking in the substance dept.
