The details of my experience are pretty much all there. I can add:
After I installed the K&N the bike felt a little sluggish all around but at higher revs is stumbled pretty bad. At higher elevation the stumble came on a little earlier and more pronounced. At a certain RPM at full throttle the bike basically stopped pulling and just made noise. If I recall correctly at lower elevation it hit at about 8000 RPM. Up higher around 7000. I put the stock filter back in and all was fine at all elevations.
I'm reasonably sure the bike has never been re-jetted. My home elevation is about 4500.
I've been very happy with K&N Filters. I've never had an experience like this with them before. I've but them in my KLR 650 and Concours within a month of getting them out of the box and they helped a lot. I immediately noticed the bike was breathing better. I did not re-jet either bike. I liked what it did to an XR600. I've had good luck with them in cars also.
Based upon my experience and limited knowledge the stock XX filter flows better than a K&N. Until someone can convince me I'm wrong I'm sticking to my opinion. I am not an expert of any kind. I am just basing it upon what we all know. Which is the air is thinner at higher elevations. The only variables I had were 2 air filters and different altitudes. Same day, same ride, same tank of gas, same wrist whacking the throttle WFO and holding it there.
Merry Chritmas all of you. Now get off the computer and go hug people you love. Thats what I'm going to do. :wink: