So that's why a 2 systems were getting crappy speeds. Yes, 2. It had been used only to split a single drop from another switch between two systems.
New drop, happy clients.
Some stuff here is museum material.
I already have a pair of Ubiquiti airMax GigaBeams left over from a different project and agree - they perform incredibly well. I didn't even bother aligning mine as they did 800Mbit/s just pointed in the right general direction. A trench was being dug to the studio for another reason and cable is relatively cheap so I figured I'd drop one in. Hasn't turned out as well as I hoped. I will setup the GigaBeams one day - but the cable does occasionally sync at 1Gbps and I'm hoping that one day it just stays there :-)