Update:
Thank you both for your contributions, they have been very helpful.
I had no idea my CPU was incompatible with my motherboard. The company that sold me my PC (Overclockers UK) is getting a very strongly worded e-mail.
I took your advice, regarding the workaround, and found something surprising/shocking. The CPU clock speed had already been set at 2800MHz, whilst the Core Performance Boost was set at 4300MHz. I hadn't changed these settings myself and they must have been made by the company that supplied my machine.
I was unsure about increasing the CPU clock above what it was set at (to the 3600MHz you suggested), so i left this unchanged, and dropped the Core Performance Boost to 3000MHz. Both of these figures are above the minimum suggested for Borderlands 2, so i figured they would suffice. Sadly, the system still crashes.
I am most likely going to heed your further advice and buy a new motherboard.
If you have any further suggestions before i make this commitment, please let me know.
Thanks again