Thank you, Batuchka and folks. Batuchka has chosen to save both by going Athlon, and with size. Hmmm, that's a pretty damn good deal, 'fastest Athlon with the 8 GB ram - hard to beat.
I could look again at mini-ATX. My main reason for full-size was number of HDs. It's not that I have a super-huge catalog. LR3 added both showing noise-reduction shown real-time at any size, and lens distortion correction; it's doing far more crunching than LR2 and isn't written for maximum efficiency. The drag's not the same on all systems. Some MacBooks made the transition from LR2 to 3, while owners of Mac Pros and quad-core PCs are pulling their hair out; they added not only the boot SSD but a third disk just for the picture cache, and RAIDed oversize data drives.
I guess I'll have to decide whether to follow suit and fill a smaller case to the gills.
One more thing (like Colombo always said) - do you think I can cannibalize the power supply out of my Dell Precision, or might there be something proprietary within the power supply's circuitry that would keep it from working correctly with non-Dell motherboards?