Utnorris: point = more quiet operation. Depends on personal preferences in each case. As to what is more important .. compact casing/better performance in most common restrictive loops because of high head pressure of DDCs and lesser power draw, or quieter operation and higher flow (in unrestrictive loops) with D5, though with bigger size, power draw, heat dissipation. I see another good point to D5s - their operating voltage range is wider then that of DDCs - easier to regulate speed by changing it in wide range then for DDCs, where minimum voltage is 8 volts, which is hard to get with using just voltages provided by molex pins (12/7/5/3) so usage of some rheobus/controller is prefered.