Since I started overclocking my October Jups via the custom firmware, I've noticed an odd issue that I never had before. Some of the VRM's seem to drop to half-power (~20w). My hashrate dips as well, but the VRM doesn't just die on me like they used to. A quick restart of the miner or adjusting/applying settings will fix the issue for a time.
Is this a heat/OC/voltage issue? I can't seem to pinpoint the cause.
Sounds like cores are shutting off. This could be heat, but more likely power or clock rate.. Use putty and BFGMiner to look at individual core performance; if you see lots of cores reporting zero you may need to experiment with volts and clock rate to keep them happy.