Well, it isn't pretty.
The computer ran overnight, so I was feeling confident. But I've returned home from work and found it off. I pressed the power-on button and the system immediately shut back down. I pulled the PCI-E power cables from both 9800GTX+, and the system stayed on a second longer. So I've removed both 9800GTX+s and booted right up with the on-board video. Note that the MB LEDs now show "GRRR" (listed Group1,2,3,4), "Early Chipset Initialization". Remember, this is with my new, better PSU.
My next plan is to attempt to run with a single PIC-E and see if I have any better success at 24-hour+ stability.
Note: I've run some CPU stress testing with success last night. I also use the Berkeley BOINC screensaver, which uses my computer to discover neutron stars (einstein.phys.uwm.edu
), so my CPU is running near full-clip all day.