Thanks for the bump on the thread.
I think the major difference is the adjustability. On the DCT pumps you have power levels 1-10, with each representing 10% of power. On the DCP pump, you can adjust from 30-100% in 1% increments. It has made tuning and adjusting my herbie style overflows very easy. It also displays the wattage that is currently being used so you know how much power you're drawing. I am currently running both of my 8000's on setting 57, which is 34 watts each.
As for silence, I know that my DCP pumps on the setting I am at are extremely silent. I have never had a DCT pump to compare, so I'm not sure if they are just as quiet or not, but Jebao advertises that the DCP is supposed to be the quietest.
I am also not sure if there is an energy efficiency gain over the DCT pumps or not. I believe that Jebao advertises that the DCP pump is supposed to be their most energy efficient model yet, but I have not compared them.
Lastly, the DCP is available in sizes up to 18500lph where the DCT I believe maxed out at 15000lph. I am pretty sure that the DCP 18000 runs on 165 watts at full power.