So finally I set up the Meshify.
Not counting the hard drives: dead silent at idle, farily quiet on load since I can run the fans pretty low and get enough air going (a bit fresher than on the R4 with running 3 intakes and 2 exhausts at 6-700 RPM). The GTX1080 is the loudest thing on load as expected, so more than quiet enough for me on load.
And the drives aren't actually too bad (can hear them just barely at about a meter away), but since I want to go with a bigger drive anyway I'm setting up a NAS on another room and making the PC 100% SDD powered.
So good results overall, count me as a fan of the open case - silent fans way of going about building a silent PC. An updated, just slightly bigger, Meshify C (Meshify C2?) instead of an S2 would've been perfect though. Too bad they haven't made it yet.