Have you tried using Apple's Network Link Conditioner (See http://nshipster.com/network-link-conditioner/ http://nshipster.com/network-link-conditioner/) to lim

Have you tried using Apple's Network Link Conditioner (See http://nshipster.com/network-link-conditioner/ http://nshipster.com/network-link-conditioner/) to limit bandwidth use by the rogue machine? After turning on iCloud Photo Library, my network was hammered for days until I used this utility to limit bandwidth usage to a fraction of what was available.