Job done, so feedback time.
New Asus P8Z77-V LX motherboard now installed together with Intel i5 3570k overclocked to a reliable 4.4GHz, and 8GB Corsair Vengeance DDR3 1600Mhz RAM. I also treated myself to an OCZ 120GB SSD for the W76 x64 Professional operating system and program files to reside on (the other four disks being the Seagate Barracudas taken from my original system). Oh, I also purchased a new AMD Radeon HD6670 graphics card (excellent VFM), and a new case, and, and, and.... So, yes, Bushfiva, with only the Antec True Power 750W PSU, those four HDDs, and the Hauppage TV card carried over, I did get pretty damn close to a completely new system
Anyway, what's it like now I have some experience with it?
It booted up first time of asking which gave me a satisfying glow having assembled a disparate pile of bits in to a living beast - followed by "please don't crash" - and it didn't, and hasn't.
Performance was clearly blazing right from the fastest Windows installation I've ever done, and it's massively quick in use.
Even with stress test relentlessly hammering those quad cores on their overclocked limit and giving the RAM a hard time, I can still web browse and play embedded Flash as if the PC is otherwise idle; no discernible lag at all.
Watching the CPU meter gadget at startup makes me smile; it merely blips a tiny bit off zero and within a couple of seconds has settled back to idle at almost zero with start-up services complete.
HDD activity whacks to 100% for about a second and a half, and then returns smartly back to an indicated zero.
Most importantly though, what's it like processing the massive Canon RAW files that originally took up to a minute and which prompted this exercise?
They now average just under 5 seconds each.
Whoo hoo. Very, very, happy.
For what it's worth, out of the maximum possible score of 7.9, the Windows Experience Index is 6.9 as driven by the lowest subscore:
Processor 7.9
Ram 7.9
Aero Graphics 6.9
Gaming Graphics 6.9
Primary HDD 7.9
Thanks again for the advice along the way.
Now, what's the next project?