Do you do a heck of a lot of climbing? If so, go for the 2.0. If not, I'd vote for the 4.0. Also, be sure to contact psimet.com to see how much he can build a pair of similar wheels (Kinlin XR-200 are like the 2.0 and XR-300 are almost as aero as the 4.0 but much lighter).
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