Probably end up as an unsolved mystery... Currently looking like a driver issue and not hardware.

I updated the firmware on the SSD (which seems to have slowed it down! max read speed is under 400mb/sec D:) and my BIOS.

Reformatted and installed Win7 x64 fresh, installed all new drivers

Reapplied my CPU (i5 2500k @ 4.6ghz) and GPU (ATI 5850 @ 875/1200) overclocks - going to leave prime95 and furmark on overnight and see if its still alive in the morning!