the cartel "skybacks" in the larger sizes have been known to dig into the calves, especially with boots that are a little lower, most of my buds who ride cartels say that rotating the highbacks helps alleviate this problem.
I also ride cartels, but as i'm in smalls the highbacks are lower and i havent had issues.
Will say though, that my idioms (japanese release co2) are some of the best softy bindings i've had.
Has em on my 3800 this past weekend ON THE GROOMERS, and had a blast! Recon said even he was impressed by the setup, I think hes now in the market for a 3800, and will probably try to snag a set of co2 highbacks for his cateks.