I never worry about security, I got sixth sense when my box maybe infected then do a restore. EOL to me is when an App you require to run no longer works. I notice a couple of website don't work with 10.9.5's Safari anymore, am able to compensate with Firefox, for now.
Gonna hold onto 10.9.5 until the bitter end, the last of its kind before all the ugly "Flat" stuff no-taste punk at Cupertino impose on us.