A very nice summation Henning and truly apprciated. Some of what you expressed mirrors my thoughts which were expressed in a post a few above yours. I agree with your summation regarding both the 90AA and the last itineration of the 90 f2.0 just before the 90AA..the latter which I also prefer for most subjects over the 90AA. Its also interesting that you go much wider on film and use your WATE...as opposed to your other camera.
I should add one additonal comment to my original posting and tests. On the M9, being full frame..at f2.8 and f4...the 90mm f2.8 Elmarit-M (last 90f2.8 released by Leica)...that lens is somewhat sharper in the corners than the 90mm f2.0 pre ASPH at closer distances...but the 90 f2.0 pre Asph has all the other attributes I described. When both are used on the M8...corner differences are negligable but each retains their particular strengths and weaknesses in all other regards.
Lastly, we have the WATE, the MATE...I've often thought one day we need a 75-90-135 lens from leica called the TATE (telephoto-Angle-Tri-Elmar). I'm sure I'm not the first one to mention this...but it would be nice fro someone to say they use the WATE, MATE & TATE! I hope no one is taking my suggestion of a TATE seriously