trivial reasons, not needed.

Can stack PCBs 1 per 80-100mm

I stacked with straight barbs but not as dense as possible.
http://i.imgur.com/xoHsaiJ.jpg
http://i.imgur.com/GXvNz3g.jpg

With 90's I could stack the Hoopiter on the left and the Nep on the right, remote the radiator and replace with single large fan.
Not that I would. but I want it to be just big enough eventually. whatever I end up with for an ASIC case.

YMMV


EDIT My hoopiter configuration has a potential flaw if I get a big air bubble in inverted waterblocks while running flat.
Designed for sitting on it side though. (that density thing again)