Heracles, if youre a SHW then go with the 13mm, it'll better help support you. If not it may take a lot longer to break in and will be stiff as a bitch (as it should). I think anyone under 200 (outline of abs can be seen) should be fine with a 10mm, but that does depend on things like how strong your core is, how hard you can push out and how "built" your low back, waist and lats are.
Also, as you might know, aim a little higher in size. I love my inzer, but they could do a better job labeling the belt size, like the fact that mine has literally 8" of prong holes, instead of the 2" range advertised. Not complaining too much about that, it would just help pick one.