As I'm back in pg code after many years, I'm feeling much better there's one (1) or two (2) items causing the hiccup. Rereading your comments, I'm agreeing with you. I'm considering bumping up the ram to 512gb as a RAM disk just for consistent profiling (an old bad habit).
I'm reassessing my profiling plan. I'm getting ahead of myself thinking the OS is not having a significant effect.
Definitely. Especially since PostgreSQL uses buffered I/O.