D5s run cooler but dumps heat back into the loop ddcs do run warm dumps heat into case instead of loop
potentially higher flow rates? not per db thats for sure and head presure is mostly up to the head wich ddc is usualy higher this chart is old but still valid http://martinsliquidlab.org/2011/03/10/pump-noise-testing-round-1/
Ive had both, original post is mostly from person experience im not sure if its the same with all ddc v d5 comparisions but my ddc is definatly quieter than my d5 not by much but its there tho both choices are not wrong there both great pumps and youll be happy wither either.