Rob, I hoping that you're monitoring the residual total chlorine in your filtered water in order to help you assess when the carbon cartridge is exhausted. That's the way we do it for our industrial clients. It's so important that there are automated monitoring equipment that constantly test that the filtered water chlorine compound concentrations are below limit. Of course that's unreasonable for a homeowner, but you can perform occassional tests with a simple swimming pool test kit to confirm if and when there is chlorine breakthrough.
I use those EP-10 carbon filters in my RO system also and they are good. They are carbon block style and they do last. The treatment mechanism between activated carbon and chlorine compounds does 'consume' the carbon material. Eventually, the carbon will be used up and it must be replaced. The Pentek site does state that this filter will remove the FREE chlorine in up to 6000 gallons of water at 1 gpm. Be aware that FREE means chlorine or hypochlorite. It specifically excludes the BOUND chlorine species such as chloramines. If your water supply has chloramines, then the 1 gpm criteria goes out the door. Then to get the desired chloramine removal, the flow rate has to be reduced to under 0.1 gpm. But the amount of water that the filter can treat should still remain consistent (6000 gal).
Understand that filter and system providers are going to provide conservative estimates of capacity and performance in this case since it means that they are going to sell more filter replacements. If you're interested in maximizing your dollars, you'll be testing and monitoring the performance of your system to assess when you really need to perform those replacements.