I don't use it, but if surface area is how you measure the efficiency of your bio media than you guys are way out of order, activated carbon has literally millions of times more surface area than any other media, 3000 to 20000 square feet of surface area PER GRAM depending on manufacturing process. Look it up.
There are many other benefits to using activated carbon, or charcoal, other than just surface area for bacteria. Activated carbon filters by means of adsorbtion rather than just straining like all other aquarium filter media. Activated Carbon can remove particles much smaller than what other types of filter media can. If you are having a problem with flow it is probably because too large of particles are passing through your other media and clogging the chambers with the carbon (this is why i dont use it).