If performance suffers from a filter that separates fine particles, it's because the filter isn't sized large enough for the engine.
K&N's biggest claim to performance increase is because it flows more air for a given filter size.
While that's important for guys that want to drop in performance instead of buying or building a larger airbox in their car (or there's not room), it's not the least bit important for applications that aren't restricted in size.
So if filter size isn't a concern, then their performance increase is negated.
Simply a matter of the filter's CFM rating that determines power gains.
If a K&N flows twice the air that a paper element will, then you'll get roughly the same power gains if you double the size of the paper element.
It's not like a K&N filter injects an oily red magical nitrous mixture into the engine LOL

I ran a K&N filter on my 250 for a few hours, then I took it off for some reason and noticed that there was sand and dust coating the intake tube and carb.
It was a brand new filter, and was oiled correctly.
Switched to a larger UNI filter and never saw debris in the carb again.
Never trusted the K&N filter, or any filter for that matter which had holes in the element 5x bigger than the grains of sand and dust that it was supposedly "filtering" out.
Sure, the oil does a lot to trap the sand and dust, but it doesn't do anything for that errant particle that gets sucked directly through that hole in the mesh, completely missing the oil-soaked element.
At least with a foam air filter there's not a direct route for the particles to follow, it has to pass through a winding tunnel of sorts (don't know what else you'd call a path through foam mesh) to get through, and with oil covering the walls of every passage you're a lot more likely to trap that particle in oil.