Comfortable pace running is whilst still being able to just about hold a conversation.
If you are huffing and puffing then you are going too fast. You should be able to maintain
this pace for 15+ minutes. If you can not then decrease pace even if it means walking.

Running at a your CP only maintains your current fitness level so if you
are looking to increase this then interval exercises are ideal for you. During intervals
your CP will be used as recovery and what will happen if you train in this manner if your
CP will get better and better as your level of fitness does.