The lab is now running Ubuntu 16.04.
One new thing is that I had expected PXE booting to 'just work', but it's been a bit hit-and-miss. I have no clear understanding why, but I might be able to find out by comparing UEFI/BIOS settings on the machines to find out what the differences are between machines that CAN PXE boot and those that CAN'T.
The machines have two distinct motherboards (ASUS H81I-plus and ASUS H97I-plus), and there are slight differences between the models' UEFI/BIOS.
Machines that can PXE boot:
NOTE: F8 should boot the machines to a boot menu that contains UEFI network booting.