I wouldn't recommend Colorado Blue Spruce unless you're okay with spraying them top to bottom with fungicide 2-3 times per year in perpetuity, even when they're 60' tall. They get needle-cast disease easier than almost any other spruce, which eventually results in defoliation and secondary coinfections, and eventual death. Norway spruce is a bit more resistant, and white pine is another option. Probably the least trouble-prone evergreen is Green Giant Arborvitae. Even fir trees seem to get needle-cast not quite as severely, although I have seen it on them as well. Not to rain on your parade, but Colorado Blue Spruce may very well go the way of the ash trees, in that none of them will survive without long-term treatment. If you wanted to improve growth rates in your spruce, try Holly Tone fertilizer.