For the teams with confirmed or marginal (Cutler, Matt Ryan) franchise QBs, a significant percent of the cap is tied up at that position. For better or for worse, the Bills do not have this 'problem' and appear to be a few years away from it. Till that time, it is fair game to spread the dollars to the rare skills and pro-bowl type performers. Dareus certainly fits that mold however his past off-field troubles stop me from advocating insane guaranteed dollars. As NoSaint advocates, it is in the Bills interest to stretch his contract and tag him till he proves himself to be trouble free. That may not be a luxury the Bills have as there are a lot of variables that come into play - Dareus holding out, other teams willing to overlook his troubles and still pay him etc.
Be that as it may, I think $51 M guaranteed for any position is ridiculous.