My Powertap wheelset uses low spoke count DT Swiss Aerolite spokes and Kinlin rims. I'm around 210 and can easily flex the rear wheel during climbs or sprints (anything above 1,400 watts). When the wheel flexes you can feel the brakes lightly scrub the sides of the rim. Aside from that, they feel very similar to my other heavy duty wheelset.
I am probably a bad example because I admittedly lack the speed of most of the 41, but I can't say one wheelset is faster than the other. The flexy set is more comfy but it could be the tires (conti gp4k). Also, the flexy wheels may not be as safe as the heavy duty set but they have not exploded yet. Will keep you guys posted! Also, I'd let your heavyweight cousin try your bike as long as he buys you new wheels if he destroys yours.