Apologies to the list members and maintainers if this is considered
off-topic and would have been better as a private e-mail. I think
it may have some merit as part of the public discussion.

I know that later on you said that you saw no reason currently to
migrate away from what you already have setup - i.e. stunnel - and
I completely understand that; anything new has to go through rigorous
reviews, validations, performance tests, etc. still, are you aware of
and have you considered https://www.tarsnap.com/spiped.html -
the spipe/spiped client/server suite? It lacks a lot of stunnel's
capabilities, but it just might possibly make up for that in
performance, which might suit your particular use case.