In alt.home.repair, on Wed, 30 Sep 2015 10:26:43 -0400,
"(PeteCresswell)" wrote:

Per Don Y:
Ethernet is also a potential problem due to exposure to lightning strikes.
Consider running optical fiber to bridge buildings. Or, protect the
ethernet drop accordingly.

OK, now MakOlber's comment is starting to soak in.

Since I know nothing about fiber - but have experience with those $150
radio links described previously - it sounds like I am going to retire
the Ethernet and dedicate that conduit to coax.

Your decision seems premature. Why not run the new line in your
conduit with the ethernet and see how they both work at the same time.

I predict they will both work fine and spending 150 will be a waste of
150. In addition wired connections are more reliable and often faster
than wireless, even when the wireless specs allow for a maximum that is
just as fast as wired. Maximum is not always (rarely?) achieved.

The remaining question seems to be grounding.