We get near 0 latency with all our Atlona/Gefen HDbaseT adapters. As a note, true HDbaseT hardware is 100% compatible with other gear. For instance I often use combinations of Atlona and Gefen gear on my shows. You just need to make sure the POE is the same voltage.
We use only Cat6 Ethernet cables and switch to copper for longer runs. My new favorite adapter is this one:
http://www.gefen.com/kvm/ext-uhd-cat5-e ... d_id=15119 as it lets us use a network (Art-Net) to control projectors over the added Ethernet connection.
If you want to know more about HDbaseT, take a look at this
page.