CI radiators work quite well with lower inlet water temps...much better than slant-fin. A CI radiator works quite well using IR radiant heating (some convection). A slant-fin works mostly by convection, and very little by radiation. Adding a door probably also means the room's heat loss will be higher, needing more heat to keep it warm than what you had. Now, what was there may have been more than what was needed. A heat load analysis is what you need to determine what's required to keep the room warm. Without knowing that, anything else is just a guess. Based on the water temp going in, you can calculate how much heat what you have now COULD produce (it's rarely on 100%), then compare that with CI radiators substituted for some of it.