The Mahle filters are at 32 microns, as far as I've been able to find out.Bypass is not at all important IMHO The oil filter's bypass will actuate just before the filter gets clogged (which is very unlikely to happen) .
What is the efficiency of the Mahle. I'm just kidding..its unknown. Most likely 95% at 40 microns where the Fram Ultra is 99% at 20 microns.
Granted that finer filtration is better. You keep tossing out that 20 micron number as if it's an unparalleled achievement by Fram, though, when Purolator and Wix both have filters at that performance level, and I'm sure there are others.
I do have to wonder where the tradeoff is. I would expect a finer filtration medium to clog faster. Of course that happens because the other filters are letting more stuff through, but if it clogs, the bypass is going to open up and let everything through. So I guess my question is, how long will it last? Do you need to change them more often?