CO-04 is contiguous across Cameron Pass between Larimer and Jackson Counties. This should not be controversial. Cameron Pass is in fact easier and more often open in winter than the very difficult Berthoud Pass between Clear Creek and Grand Counties that is the only route connecting the two parts of CO-02 on the current map.
Fort Collins to Steamboat, 157 miles 3H 31M (73% longer) over both Cameron and Rabbit Ears passes.
Even if you insist that the route stay within CD-2 (via Nederland up Boulder Canyon and the Peak-to-Peak Highway) it is only 114 miles and 2H 32M.
I don't see what Berthoud Pass has to do with anything.
And your circuitous connection from Springfield to Montrose is 750 miles and 13-1/2 hours. This is double the distance and time of a direct route instead over Monarch Pass and almost the entire route on US 50.
Even if you were only talking about Fort Collins to Grand Junction, you would drive through Denver and save 2 hours rather than using Cameron Pass.
Why not include all of Jefferson county with CD-6? Will that make any difference? What if you added Pueblo with CD-5 or CD-4?
