For what I remember, the MTF curves used to be on the official site
but they seem no longer. (I for one don't care!)
And yes, Erwin did test the humongous
As far as I understand, he is much less scathing than my reference of the time, the French magazine Chasseur d'Images
I am personally extremely pleased with the 1.9/28 (both the object and the pictures taken through it).