I have actually been very happy with mine. I too am a fairly aggressive rider and weigh 180 lbs. I have never experienced any flex that the above posts mention. These wheels have taken some pretty big hits on the crappy post-winter pavement around St. Louis and have stayed perfectly true. I was thinking about getting the Mavic Cosmos too, and if memory serves me correctly, the wheelsets are within a few grams of each other in weight. Having not ridden both, I can't comment on the Mavics, but the 540's are very good, solid wheels that give some aero advantage over "standard" wheels. Just my .02