Well, 2 years later and the saga still continues.
Since the last posts, I've replaced the Gigabyte Z77-D3H with an Asus P8Z77-V, I've used a new SSD with W10 installed, and I'm also currently using my mates set of DDR3 RAM, all to no avail.
Honestly, the only thing that hasn't been swapped out, or replaced, or tested with equivalents is the CPU, the i5-3750k, and even then that's had a fair few tests of Prime thrown at it without any problems indicated.
Completely at my wits end. I'm honestly just going to price up a new completely fresh change of hardware, and move to a completely different socket. I've had nothing but issues ever since I went onto 1155 from my old 775 Q6600 system.