user283746

I'm an EE that did power optimization at Qualcomm a while back. I'll just say - if only it were that easy ! If everything lines up, yes, it's possible to drop power draw to ideal. But clearly the software (legacy vs new kernel) heavily influences actual physical temperatures on the same silicon/processor. So safe to assume the board (design, layout, components etc) is just about acceptable for this price point, even if not optimal.
 
Without a specific deep-dive into this issue, our efforts here are like band-aids the minimize the thermal performance problem with 4.x kernels rather than solve the problem at the root cause itself. IMHO, these are all 'toys' so I don't see anyone 'caring' enough to root-cause this (vs say, if this was my product line). Tinker on!

@chwe Your CPU underclock instructions work and it helps to some extent. Board is still a lot warmer on newer software than legacy, so I'd also like to underclock the RAM.
 
How do we underclock ram?

FYI, I also changed the governor to powersave which also seems to help. For anyone more interested in governors here is the link to kernel docs. Documenting here for future readers, note that lines starting with # are commented out
user@orangepizero:~$ sudo nano /etc/default/cpufrequtils # WARNING: this file will be replaced on board support package (linux-root-...) upgrade ENABLE=true MIN_SPEED=240000 # MAX_SPEED=1200000 MAX_SPEED=816000 # Run at lowest # GOVERNOR=powersave # Dynamic, jump to max # GOVERNOR=ondemand # Dynamic, slowly scale up GOVERNOR=conservative user@orangepizero:~$  sudo /etc/init.d/cpufrequtils restart Lastly, you can see with 
sudo cpufreq-info and set (NOTE  - this doesn't persist across reboots, so use the /etc/default/cpufrequtils file for persistence)
sudo cpufreq-set --max 816MHz