I put GP4000s on my bike this fall. They've only got about 800 miles so far, but what I noticed right away is that they have a much more uniformly rounded profile than the Michelin Lithions that I'd been riding. The Contis turn in much easier, but they definitely feel twitchier for straight-line riding. That also means that, similar to motorcycle tires ridden on too much freeway, the profile will change over time as they wear a "flat spot" in the middle. (I'm pretty sure unless you only ride crits, there's no way to wear bici tires uniformly on the sides... and these aren't really race tires. )

This isn't pro or con, just an observation of how the feel of these tires differs from the Michelins.