You would fit either so your choice would be based on whether you want a higher BB and thus lower handlebars (150mm), or a lower BB (100mm). Aero and learning curve would factor in. The sizing chart is for 100mm extension. Look at several of our pics and our given X-seams to help decide. I think even with the 150mm extension your BB would not be as high as mine (100mm 42" x-seam).