@tgilly If you'd like to diagnose the problem, then you'd have to provide the necessary info. No, I don't think 4.4 is unstable, but your problems look like a power supply problem, the system throttling itself down automatically, or more related to the fact that your ROM folder is mounted over the network.
Check if your power supply is right up to the specs and then try running the ROMs from the sd card for a test to see if you get the same symptoms.
Please do not post a support request without first reading and following the advice in https://retropie.org.uk/forum/topic/3/read-this-first