D5 is imo the better pump, its variable either through speed settings or pwm is generally regarded as quieter and has less problems with overheating although im not sure how big an issue that last bit actually is, however its large, like twice the size of the ddc. Performance wise they trade blows and both have more than enough grunt to run most systems. Theres no right or wrong option but if your tight for space get the ddc if you want something you can tune to your system and noise / performance requirements get the d5