I really appreciate all of the input and opinions. Perfectly considered insights, exactly what I needed, and hopefully it helps someone in the future who is weighing a large (for me) purchase of a used device that will need to last 6yrs or so.
rndmE
I personally would not know how to bring even the 6a into its performance limit.
This is exactly how I look at it, the 6a is enough for me. I felt the same about the 3a... such a shame to give up on these devices due to arbitrary EOL (although I do understand the device/support/dev/lifecycle game).
It seems the 8a is the device for me. Aesthetic/design matters little, and I think the performance gap to the 9 is something I would never notice/appreciate.
Many thanks to all who provided their insight :)