Paragon, I tried a Seasonic X-760 both on the old and new motherboards -- see my post above.
Board was just under a year old -- replaced back in the whole SATA corruption recall in March 2011. P8P67 Pro board is dead -- tried it with the new processor and it still exhibits the same symptoms...
well, to all the googlers out there who want to find out how this story ends:
My P8P67 Pro went south and killed my 2500K in the process. Tried out a new 2500K in the P8Z68-V/Gen3 and it booted up without a hitch.
For reference: http://www.techpowerup.com/forums/showthread.php?t=155296...
The System:
Antec P182
i5-2500K (oc'ed turbo boost to 4.4ghz)
Thermalright Ultra 120 Extreme
G.Skill DDR3 1600 (2 x 4gb)
P8P67 PRO (rev3) --> P8Z68-V/GEN3
Corsair HX520
Probably not exactly thinking straight after spending a sleepless night trying to decipher this issue, but I'll try my...