Thank you. Backed up and done. Flashed my secondary C7 v4 with the 1GHz CPU only mod as that's what QCA9563 seems to reliably do on stock voltage seeing gwlim's sample and looking around on Google. Not touching memory as I can't control timings/voltage to stabilize.
Given that it hasn't rebooted on some browsing and torrenting... doing some preliminary testing with my phone and the wifi sweetspots app that tests maximum throughput on wifi links:
5GHz on a 2x2 phone at ~2m, direct LOS to the router
Stock: ~530 mbps
1000MHz: ~620 mbps
Nice improvement. Any extra CPU power out of these single core devices is more than welcome.
If it remains stable then I'll flash my primary C7 v4 which runs a 50/10 mbps PPPoE service on a fiber link while doing SQM on it, plus all the other routing tasks. There it'll be more noticeable. I have some spare heatsinks I'll be adding shortly.
Thank you very much!
edit: flashed the other C7 v4 a few hours later.
Three days so far: no abnormal behaviors at 1GHz, downloaded file hashes all match, heavy torrenting heats up the chassis a bit more than before, but other than that, no downsides.