Your window is coming up, if you wait until October you are taking a chance of cold/wet/frozen riding in Colorado, plus daylight hours are shrinking. When you consider your lodging options, you're booking in advance usually, meaning you have to remain on the schedule, and if you bite off more than you can chew, the whole schedule gets fouled. 350 miles per day plus or minus 50 is about the limit I plan for, although my 2,000 mile 2 state trip was almost exclusively mountains and canyon, glorious! I started each day early and wanted to arrive by late afternoon to get cooled down, settle in, relax over dinner, beverage, and turn in early. I packed as light as I could out of necessity, do not have the bags so packing would take me a while longer, bungie'd behind me but carried all I needed. Very little rain to contend with but temps varied from 104-37F. My MSR ISDE Gore-Tex jacket and Pants served well, airy and dry, warm or cool when it had to be. The cruise control was a big help in allowing me to move around, sit upright, stand etc. The heated grips too, when your hands are warm, the warmth flows through your torso. With a fleece collar, I was surprised how comfortable I could remain even when it was below 40 degrees. The Bridgestone S22 tires felt soft and planted at all times, excellent grip and life. I think if you have to make 450-500 miles daily, you are forcing the limits of endurance, darkness and chance, and it will cease to be fun.
I had considered making this trip on my KLR650 as an adventure bike, which would have been great fun also. That bike lacks the cruise control and heated grips but has an all day comfort upright riding position, plenty of room on the wide seat to move about, the fairing offers less wind protection to your torso but your hands are still out of the wind because of the hand guards. I would have gained range between fill-ups and the option to explore off-road but what I would have given up, was that rush of supercharged passing power to get around those long lines of stacked cars, trucks and motorhomes, which really shortened the trip, nice! I don't think you should count on making up a lot of time speeding on the interstate though, you'll just get nailed for it.