There are 2 shadow of the rockies routes---you didn't mention which one---but after I thought about it the gas thing is the same for both----------you have enough gas to be OK.
However you have not allowed for something that I always make a priority.
What if ???? YOu have to re-route for a closed or impassable road ???
What if you hit a road that is washed out -----you have to back track 50 miles---then find another way ????
What if you crash and lose a little gas---I've had that happen several times.
What if a gas station is out of gas or isn't open ????
Having a 300 mile or more range is much smarter.
And if you are worried about the weight of an extra 2 gallons of gas that you may never use----think about the weight
of a 400----to 700 lb. motorcycle you'll be pushing if you run out. You'll make it about 13 ft.
With limited fuel you may run into a situation where the trail goes right-----------but your gas tank says you better go left for fuel---------I hate that.
I loved both the shadow of the rockies routes-----the New Mexico one was my favorite as it was more remote and far less people and towns.
And you can run the New Mexico route much earlier in the year than Colorado---as the snow melts off much earlier-------seems I rode it in March I think ?
KTM EXC 450 2006
Husqvarna TR650 Terra 2013
KTM 690 Enduro 2014