Wix is back up. More hocus-pocus mumbo-jumbo from them IMO. How can they state those two filters you linked are "2/20=6/20" and then call it "5um nominal"? 5 does not equal 6, after all. Most everyone accepts that "nominal" means 50%. How can you be "nominal" at 5um, but beta 2 at 6? The math does not work.
They have changed their filters over the years. It used to be that their offering for the HD TC engines was the 51348 (equivalent to the MC 910).
My point is that Harley calls their filter a "5um" filter, but never tells us what efficiency it offers at that particle size. Those who understand filtration know they are only telling 1/2 of the info we need to understand their filter performance. With rare exception just about any "normal" filter we can buy, even lowly filters, can be "5um" rated. Probably really bad efficiency at 5um, but they will catch a few in their life-cycle.
Think of it this way; I can probably catch a few 100-mph fast balls from a major league pitcher. Not a lot; maybe a few out of 100 thrown. But I can claim to be a "100mph" catcher. Same goes for filters. Telling me a some arbitrary particle size means nothing unless you tell me how efficient you are at that size.
I'd like to see the entire filter industry start rating automotive type filters at 2/20/75 (nom, decent, absolute). But they don't ask for my opinion.