MUG, I enjoy reading your thoughts on the DB situation, and I think that the talent that we have among our second tier CBs is an interesting conundrum when constructing the final roster.
However, IMO, your analysis overvalues Boldin. While Carter and Harris have already produced (and produced very well) for the Broncos on the field, Boldin really hasn't done much. He's been an ST player that occasionally gets reps on Defense, but by my estimation, hasn't done anything of note in either situation.
So if it came down to Boldin vs Carter, my own inclination would be to pick Carter over him. But of course there is the matter of a 4th round "investment" in Boldin, but to me, that draft status isn't high enough to preclude keeping the more proven player (in this case Carter) or drafting a blue-chip player in this year's draft. Of course, JFox and Co. don't make it easy to read the tea leaves since they are notorious about underplaying rookies and then unleashing them later on!