Elliot, Mounting the center channel lower puts it in front of the wood burning fireplace. Wife vetoes this approach on aesthetic grounds. (We have great memories of burning logs last Xmas when we purchased the house.)
Erik, The TV mount is a MantelMount 540. It pulls down 27", which puts the center of the TV right at eye level while sitting on the couch, assuming a 5" high center channel speaker hanging below the TV.
The TV is an OLED65C2PUA. If I had considered possibly not using a receiver before I bought the LG, I probably would have purchased the Sony Bravia instead, and just added a sub.