at ~13% of the full load, or 50% of one (out of four) core(s), tested using iperf.
it's x86, use the regular x86_64 builds.
Fan isn't very loud, it's about the size of a 8 port desktop switch, 1U high though,
which is pretty much the same as any regular 4+1 port home router, antennas excluded.
See Cyberoam CR25iNG / CR25WiNG wired router HW discovery for additional info.