I thought it was my incompetence that rendered my computer inoperable, but in fact it turns out that my motherboard, the Gigabyte GA-P35-DS3L, is known to sometimes fall into a state of constantly rebooting – the entire line, in fact. See here, here, and in particular here.
So for my new purchase, I asked for a non-Gigabyte recommendation from my local Canada Computers, and got the ASUS P5K-E/WiFi-AP motherboard instead. It’s about twice the price of the GA-P35-DS3L – itself the low end of that line – but I didn’t want to invite more mishap by picking a low-end family, regardless of brand.
Replacing the motherboard solved my rebooting woes, and a strange might think that after my troubles, I would leave well enough alone. Not at all. 
Knowing now, that it was not my tweaking efforts that was the root problem, I resumed my overclocking attempts.
Notable highlights working with the ASUS P5K-E/WiFi-AP:
- The length of the eVGA GeForce 8800 video card was enough to block one of the SATA connectors. Poor design on ASUS’ part, since my previous motherboard didn’t have this problem.
- Able to overclock my Xeon E3110 from stock 3.0 GHz to 3.6 GHz. Based on Internet readings, I can’t get much higher due to the CPU, rather than the board.
- Automatic overclocking BIOS works surprisingly well. I constructed a simple timing test, and the BIOS got ~15% boost on its own, compared to ~25% timing improvement manually.
- Has a lot of overclocking options: voltages, speeds, etc. Defaults to an automatic setting rather than a fixed value for all of them.
- CPU fan speed control didn’t work with Ubuntu (pre-release Hardy 8.04), even with the appropriate BIOS settings. Strangely, the same operating system install had no problem with the GA-P35-DS3L.
- WiFi works like a charm on Linux (uncommon in my experience).
