I have had the new C4's since they came to market and LOVE them. The only thing I didn't love was their nylon slings. They were short, too short. So, from day one I got them reslung with a double length nylon runner from Forrest. It was cheep and they offered colored slings to to match the cam and the anodized Nutrino biners to boot! So, my whole rack from .5 to number 4 are all doubled. It is about time to get them reslung and I can't find Forrest on the internet in my 5 minutes to searching to see if they will do it again. Any help???
BUT, note BD doesn't double sling them for a reason. As they are doubled, the nylon rubs over itself on the thumb loop. When you fall the nylon will rub over itself in the extended position and possibly melt if enough force/friction is generated. I don't believe that it is a real issue for smaller, lower factor falls, but the 1.5 and up and you will have some issues. I have take a fall on my .5 and have retired it to the wall until I get them reslung, hopefully soon. Correct me if I am wrong.
The new DMM Dragon cams addressed this issue but putting the double length slings through separate holes on the stem. In their original release of the cam at OR a year ago or so the double sling was around the thumb loop. (like the C4, but changed for production; http://www.dmmclimbing.com/news.asp?nid=216&ngroup=1) I personally hate the non thumb looped stem of the dragons and older C4's, as I believe for a gloved hand they suck. So, DMM must have smartened up, as going to production with that potential talking point/issues for many more climbers then just I would open up a huge nest of problems/people on the internet bitching...Or, they got a drop tower and did a few Factor 2's and melted through their skinny little spectra cord that they currently use.
So, what do I win for that trade off in potentially melting some nylon??? I carry less alpine slings=less overall weight to climb up a mountain with.