Rhinoman I've always respected your opinions and knowledge, and would tend to agree with you on this except for one thing: you seem to contradict yourself when stating " they are rubbish at filtering dust and fine particles" then later in the same sentence you state:" for outright flow, then clean and oiled they are probably the best filter." I use K+N filters particularly because they are CLEANABLE, easily actually, and easy to re oil. Now I may agree that ultra fine dust may get by , but if its that fine it's not going to do any real damage to the motor, especially if you observe regular oil changes with good oil. I've also done dyno comparisons between K+N, Harley's own performance brand Screaming eagle, and stock filters, and the K+N out performs all, properly clean and oiled. Who would put one in not properly cleaned and oiled? I probably wouldn't use one on a pure dirt ( motocross/enduro) bike, only because it would require more maintenance. The oiled foam filters are better at keeping out water from the airbox too, but clog up real fast. I had a Calmini oiled foam filter, and found a noticeable increase in throttle response when I switched to K+N. Besides, Calmini has no real instructions on cleaning and oiling there filters, and when I asked the sales rep he said NO oil. Might as well stuff the airbox with a rag.
PS, on my old road race bikes we used velocity stacks, air filter? what air filter! Of course today's bikes have sophisticated air boxes and really good breathing systems so an air filter really doesn't hurt flow too much. OH, and did you buy anything from "BOB"?