Sorry for the huge reply lag; real life kind of caught up with me.
Re chirping: I'm almost positive now that your guess 1 is correct.
What I've done with overclock so far is set my multiplier to 17x (3400MHz) for normal use, and 19x (3800MHz) for Turbo. I've also undervolted the processor by 0.025V (I think; don't want to reboot and get into the BIOS right now to check that). The reason being, voltage increases proportional to clock speed. At 3800MHz, it thinks a "normal" voltage is 1.475V, instead of the 1.3V or whatever it normally expects for Turbo. Voltage goes down again as the processor throttles back; the modest undervolt is the most I could do and have the processor stable at its 800MHz idle frequency. It runs at 1.225V at that frequency. I don't think my motherboard's BIOS has an option to disable this feature. It may be linked to AMD's Cool'n'Quiet, but I don't want to get rid of that.
Anyway, the reason I'm using high Turbo clocks and not increasing the main clock multiplier much is for power and heat reasons. Not so much the processor, though: temperature readings say it idles at a minimum of 18.88°C (almost exactly room temperature; just barely believable considering the CPU HSF draws most of its intake air directly from outside the case) and I'm getting a max of 38.12°C over both three-core Turbo and six-core regular loads, which is nowhere near concern levels. Unless the temperature sensors on all six cores are reading consistently low, that is. I'm not too skeptical of this, because I can touch anywhere on the CPU heatsink during a load test and it's no more than mildly warm.
The problem, however, lies elsewhere in my case. TMPIN0 reads a min (idle) of 35°C and max of 41°C; TMPIN1 reads a min of 31°C and a max of 48°C; and TMPIN2 reads a min of 39°C and a max of 55°C. I've seen TMPIN2 up to 61°C during higher-clocked (18x) six-core loads.
It would be nice to know exactly where on the motherboard these sensors are, but I have my guesses. I'm guessing northbridge, southbridge, and VRMs, in that order, based on the highly scientific finger test. Since I have a low-noise (and thus low-airflow) computer, none of these components gets much airflow. The VRMs in particular are in kind of a dead spot for airflow, and they're un-heatsinked to boot. Even though I have a down-flowing CPU fan, the airflow through the heatsink is pretty slow even at high CPU load, and it's immediately exhausted out the rear of the case by the rear case fan.
It would be nice to get these components some air, which might allow me to raise the main multiplier that much more. I don't want to sacrifice silence to do it, though. I have an intake fan in the front of the case, which blows air over the HDDs (which remain cool to the touch). I'm thinking of moving that directly below the CPU fan, which should point some air at the NB and SB. I don't know how that'll affect HDD temperatures, but I plan to migrate mostly to an SSD fairly soon, so that might be a mitigating factor (the HDDs will still see some use, but only when I'm running backups or accessing files too large to keep on the SSD). The other problem with this is there's not actually a place designed to mount a fan where I want to put it, and it's in the middle of a flimsy panel so I might have to cook up some reinforcements to keep it from vibrating and making noise.
The VRMs, I'm not too sure what to do with. They're in an awkward position to route airflow to with any kind of fan, since they're mostly occluded by the side of the CPU heatsink. I suppose I could buy some of those stick-on heatsinks (like so).
That won't get any more airflow up in there, but maybe convection and increased dissipative surface area will do its part.
Memory is also pretty warm, but not uncomfortable to the touch like the components I'm concerned about.
Thoughts? Ideas? Am I worrying about nothing?