They can move quite a bit of air at high RPMs, at least the 40mm fans our servers use at work lol.
Also, on a side note, we ordered 2x new test environment rigs for various uses:
Xeon E3-1245v3
Intel DH87RL
4x8GB Kingston ValueRAM 1600MHz CL11 1.5v
Seagate 1TB SSHD
Corsair VS350
Bitfenix Prodigy white
Assembling them as soon as they arrive, build post coming.