Just a small update. I have re-formatted the quad-GPU cruncher, and installed Win7 64-bit instead of XP, and instead of running F@H, I'm running PrimeGrid under BOINC.
Had a little issue getting BOINC to recognize all four GPUs, but that was solved quickly.
http://forums.anandtech.com/showthread.php?t=2205059
I upgraded (side-graded) my PSU, from an Antec EarthWatts 650W with a pair of PCI-E 6-pin splitters (PSU only had two PCI-E power plugs, needed four for all four GPUs), to a Xion "PowerReal" 800W, which has four native PCI-E power plugs. (On only two sets of wires, coming from the PSU, not sure if I like that.) Also, the Xion PSU, has a voltage-selector switch, so it's an older non-PFC design, probably not as good efficiency as the Antec.
Found out recently, that Newegg has PNY GT240 GDDR5 512MB PCI-E x16 cards for $40, no rebate. These cards are essentially die-shrunk 9600GSOs. They have 96 SP, just like the older 9600GSOs that I'm using. The benefit is, they don't take an extra PCI-E power connector, they are powered solely by the PCI-E slot.
I figure that's both good and bad. Good, because they take less power, so my electric bill would be less for the same amount of crunching. Bad, because I don't know if my PCI-E ports can power FOUR cards. I think that the K9A2 Plat. board does have an additional molex connector plugged in near the PCI-E slots to power them additionally, but I still wonder. Especially if I tried to overclock the video cards slightly.
As it is now, I don't really have to worry about the cards burning out the mobo's slots.
The only real reason I would consider spending $160 to replace all four cards, is they would be quieter, one of my cards overheated due to a software bug in Precision, and the fan on GPU0 is now a bit noisy, but it still cools adequately.