10K urban run
The costs associated with regular extended aerobic training are decreased speed, power, and strength, not to mention health and fitness. Reserve your longer, lower-intensity "cardio" training for recovery from intense work cycles, when you can no longer deliver on the high outputs that CrossFit demands.
You CrossFitters do primarily short-duration, high-intensity training in the anaerobic pathway, yet you can still perform in the aerobic realm. How many of the endurance-sport crowd can do what you do here every day? How many have the capacity to execute randomized, multi-joint, high-output movements with precision and power?
"Farther, longer is not fitter, is not healthier." - Greg Glassman