Sorry but I have to agree.
The 680i is a terrible overclocker.
Things you can try in order to get it stable...
Give the CPU more voltage.
Give the Northbridge more voltage.
Give the Southbridge more voltage.
Test your memory with Memtest
and, if it fails, give the memory more voltage/relax the timings.
Keep an eye on the temps.
They should never go over 75c load.
Best luck getting it more stable.