When I got my new bike I found that after about 25miles my neck hurt. I went through 2 fittings which ultimately added a stem that was more angled and that made it better but on long rides my neck is still sore sometimes (I do have neck issues which are unrelated to cycling). While my old bike is as tall and the dimensions are remarkably similar there is something in the geometry that made it more uncomfortable. In my case I believe it was due to going from tube shifters to the newer intergrated brake/shifters which had me spending more time with my hands on the hoods than I ever used to and therefore had me bending my neck more than before for longer periods of time This was not the case for me as it had more to do with a neck that simply isn't flexible enough. If I concentrate on not doing that I find I have much less issues but if I am doing a lot of climbing/harder riding I tend to forget...especially if I get tired