Up to date conventional wisdom re max shared_buffer size?

Briefly, just curious if legacy max values for shared_buffers have
scaled up since 8G was like 25% of RAM?

Pg 9.3 on monster 2T/192 CPU Xenial thrashing

Upgrade pending but we recently started having $interesting performance
issues at times looking like I/O slowness and other times apparently
causing CPU spins.

The DB is 10TB total size with OLTP plus some occasional heavy batching
which frequently correlates with degradation that requires intervention.

Unrelated server problem forced us to relocate from a Debian/Wheezy 3.x
kernel 1T 144 CPU to the even bigger box mentioned earlier. And we wen
up a major kernel version also in the process.

Anyway, shared_buffer coherency generally high but does take big dips
that are sometimes sustained for seconds or even minutes.

shared_buffers only 20G which is relatively very small vs total machine
RAM however we do not have the luxury of scheduled downtime so this and
other settings requiring a full restart are not touched without good
reason.

Thanks

--
Jerry Sievers
Postgres DBA/Development Consulting
e: postgres(dot)consulting(at)comcast(dot)net
p: 312.241.7800