The DDC is not a bad pump but can be a bit of a pain to dampen properly (or rather: can be quite noisy when not dampened properly), and is noisier than a D5 even in a proper setup.
Given that they cost pretty much the same (at least where I live) I'd recommend the D5 unless you're working in a really tight environment.
The D5 has ample power for the loop you're intending to do, and should be pretty much inaudible through the fans when dampened properly and mounted inside a case. On full speed it does produce a little bit of a hissing sound, but it's a lot less noticeable than the corresponding emission of a DDC. On speed setting 3 of 5 (at 12 V), I can just hear it when it's running on my table in the open, but even one silent fan will be louder.