So what could it run if the room is about -30C or lower?
Condensation, so... 0GH

Am I right in thinking that your top SP31 is sucking in air from the PSU side, but the SP20s and S5 are doing the opposite and throwing air out?
Doesn't that get a little 'circular' ?
no they are all blowing the same direction
You can quickly remember which way a fan is blowing as they always blow towards their frame.