I have been able to swap out the power supply (similar Corsair), DDR3 RAM with the same (Corsair) modules, graphics card (new last week) and the same random re-boot behaviour persists. The fault shows up when running Win XP or any of several versions of Unix. It misbehaves when booted from USB stick, hard disk or from CD Rom. It can reboot before the POST has completed but some days, it will power up and run all day without problem.
The other machine I borrow parts from is an AMD Phenom and the iffy machine is i7 930 1366 socket. The incidences of spontaneous re-boots are getting more frequent (perhaps caused by static damage?) and do seem to be more likely to occur when playing video material (Youtube or even news), I don't do gaming. I am inclined to think that the motherboard is more likely to develop a fault that is PC task related than the CPU chip is.
I don't have access to another machine with an i7 1366 or a one with an 1366 motherboard to do part swapping so I can't diagnose further without spending money. I am wondering whether to just bite the bullet and buy new CPU, motherboard and RAM. The second hand prices of 1366 motherboards are a lot higher than I expected, more than the new price either now or when I bought the existing one.
Rans6.........