Swapped the rotors over and ran them today on my Canfield Riot. Trails where pretty much all natural with some rutted out sections and a few berms strewn about.
To be honest there's not much difference between the two. Normal riding? You couldn't tell. Start hitting those really rutted sections hard and the carbon wheels seem to hold their line better (less pinging off things?). The biggest difference came in fast bermed corners, where you could feel some compliance in the rear wheel when cornering hard. Note that I'm on a 29er so they are going to be more prone to lateral movement than the smaller wheel sizes.
Overall I don't think the carbon hoops are worth double the cost. If I smashed an alloy rim? 100 bucks and a re-lace. My Zelvys have crash replacement warranty so it wouldn't be crazy expensive but once warranty had run out it'd be a different story. End of the day, the carbon wheels are better, but as with everything, it has a price premium.
Happy with my Arc 30s