I have a 14 and I like it for it's ease of pointing. Since I have a RF breech I am able to use the whole top tube and my L stock for pointing, and it's great for me. I guess my biggest complaint is not being able to use the velocity adjuster rod, since I have to unscrew the barrel every time.
I don't think there is much of a difference in terms of efficiency or noise. Might be a little quieter, but that is not an issue at all. Also, the 11 is notably more compact, but I play woodsball so it's not a hindrance much.
So my biggest complaint is not being able to use the rod. I'd be really happy if mike was able to make/find a rod that is long enough for the 14.
Hm, all the rods I get are long enough for the 14", which I prefer to use with my open class Phantom btw.
Did you buy yours used? Maybe so cut it?!