If Stevie hits but Bryce doesn't then it's a 2016 4th from Buffalo.
Basically, the Bills should hope that Stevie doesn't do well in 2014, because I doubt Brown will have much opportunity to put up numbers that will move it to a third round pick. That way the pick is gone from San Fran, which will be a low fourth anyways, and you can have Bryce Brown play well in 2015 without worrying about it costing you a higher selection.