I have an '06 KLX250 with a 300 cylinder, but we're talking fairly close stuff here. I have a Dynojet kit, as I feel the stock needle just has a bad performance profile. I have all the airbox mods with a full Muzzy exhaust. I think you'll find most any bike down on power when you start hitting the really high passes like Imogene...over 13K...and others, but good jetting at home usually works quite well with our CV carb setup...unless perhaps you're coming from sea level. Your pilot sounds a little rich to me. When I had the full Muzzy with all the airbox mods and DJ kit, I was running the OEM 35 pilot. When I went to the 300 cylinder I installed a 38, and it was too rich. I went back to the 35, and it was perfect. A Kouba air/fuel idle mixture screw helps a lot when you go to CO, because I find the idle to be affected the most when approaching the tops of the passes. I'm running a DJ main jet that is 128, but that jet doesn't exactly match the Keihin equivalent. Honestly, I think it's worth the money to get the DJ kit if for nothing else but the needle. Throttle response and the point on the needle for cruising is just better all around IMO. I still get great mileage too. I live at 1700' here in Texas, and I have never changed the jetting for CO on this KLX or my KLR600/650's with CV carbs in over 30 years of going there. If your jetting is clean and crisp at home in Ark, I think you should be fine. The down on power feel will occur regardless, but it should run cleanly. I think you can safely go to a 35 pilot for sure and maybe turn in the mixture screw when you get there.