I personally find that I need to stay with bars no wider than my shoulders - 40 - otherwise I get upper back/shoulder soreness. I swapped out the stock Bontrager that came with my Madone for a FSA model, suggested by a bike fitter, that measures 40 but the drops flare in ever so slightly making the tops a 40 but the drops more like 39.5, and this has been very comfy for me.