Originally Posted by Ground Hog

OK, let me explain a bit more, I am going the custom route because I can't get a frame that will give me the handlebar height that I need without having to use a pile of spacers or a problem solver stem extender like I'm currently using on my cf bike.

Why 650b's? In order to get the handle bars higher the headtube has to be longer and the top tube must have some slope, at a certain point the standover height becomes too great. 650b's allow me to run wider tires at around the same nominal diameter as 700 x 23 tires and keeps the top tube lower. The 650b also allows me to run wider tires and fenders with less danger of toe overlap a common problem with smaller frames.

I'm not short but I want drop bars for the multiple hand positions but I don't want to be bent over or stretched out, custom is the only way to meet my needs. The selection of decent road tires in a 26" tire is limited.
Finally if you talk to Peter Weigle and some others they will tell you 650b is the way to go. There are many in the MTB community who love 650b and find it's size to be just right hence the accessibility of 650b disc wheels and 650b wheels with 135mm rear spacing.