I'm not sure about CE Reactors but a Westinghouse 4 Loop Reactor can shed about 30% load extremely fast during a runback, BUT so much active stuff happens you really have to be on your toes, Rods insert, Steam Dumps Open, Spray Valves open, the turbine sheds load and in many cases you end up Emergency Borating. The two Runbacks I had at Fermi and the time the HTR Drain Pump tripped the plant ran back, stabilized and that was that.
On the OTHER hand, The ECCS was complicated as heck and was required in about every mode. One thing I like about PWR Tech Specs, once the plant is cold about all your major Tech Specs are non applicable.
Mike