"But Richard just said the M90 has 950 mmH2O, need 1500 mmH2O to be rainproof, maybe 950 is good enough.
When I take M50 and puddle water on the top of it 1/4 inch deep, for several days, there is no leakage. I've had M50 sleeping bag get wet from dew and the down inside absorbed no water."
True, but those are results from a static test. For real world conditions, you have to factor in dynamic conditions and aging. And I've once read a test wherin some fabrics had an initial HH of more then 5000 mm and after only 6 months UV-exposure it dropped to less then 1500 mm.
"Experienced people say that if it rains enough and you're exercising, eventually you'll get wet, even with best membranes"
Sure, I can even get wet if exercising intensely while wearing nothing. So you can then get everything wet.
"Maybe DWR is sufficient."
Well, sometimes I prefer my only water repellant windshell in rain (even if it's heavy), but as often (or even more) I'm glad to have a waterproof shell.