Some update:
I have not updated the BIOS, but I did figure out how to make the case fans that are controlled by the MB run, that being to set the control temp for them down lower...apparently by default they don't come on until the MB reaches like 80C or something, and the "don't go below 30% of max RPM" doesn't actually do anything...perhaps because the MB has no way of knowing just what 30% of "max" would be? I dunno.
But anyway, the fans (2) run (1140 RPM right now) and have for days (uptime says 2.5 days now), and the air being pumped out of the case is 91.8F and ambient is 73F.
I've rebooted the machine and it no longer does the odd behavior I cited earlier...nothing was changed physically, I only went in and futzed with the fan settings in the BIOS before rebooting. After a week of running without any problems I felt confident that I could mess with it some and see if it'd "do that again" kind of thing, and it didn't. So no youtube for now.
I did have the case open...maybe I bumped something in the right direction...reseated a card or something. Not intentionally though.
Oddly though, instead of running at 118F like previously, the card now runs at 152F which is sort of odd; it's pretty much like the other card (with a single fan). With the case fans running and the output temp of the box now 10 degree F lower, I don't know how to explain why the card is running warmer and "better".
I guess there's no way to monitor the PS utilization; like if it was being overloaded or not.
Maybe the PS is the part that doesn't like being 100F and was carking at that, although it's supposed to have a PWM fan that I thought would ramp up in RPM if it didn't like the temp.
Anyway, I guess I'm a "happy customer" now. I'm going to guess that my original issue with the HIS card and DVI-1 (actually both DVIs were black until I rebooted, but only DVI-0 came back) was something to do with a) heat, and b) the xf86 driver (OSS) not handling DPMS very well (which I've since disabled - again - a lot of people have trouble with it).
Thanks for everyone's input though. Appreciate your time. The next box I build that I intend for this kind of "always on" use I'll do a little more research into I suppose (heat, parts, ECC memory, power supplies, cosmic rays, whatever).
Regards,
--kh