[MemoryReaction] G.Skill F2-8000CL5D-4GBPQ - Low in cost, high in speed!

[Cronos]

First thing you always MUST be doing is memtest86+. Current version is 2.0
http://www.memtest.org/

First pass tests 1-5, if no errors, try test 5 alone 10+ times. To iron out, pass the whole default set of tests 10+ times.

After this, try Linpack 64bit, problem size 30000, 100+ times. Good chance it will find some errors Memtest86+ missed.

P.S.
Don't forget to check the real vDIMM voltage. Many boards overvolt by default. Many ASUS boards overvolt by 0.05V.
And i wish you luck with 680i board, 680i is probably the most troublesome chipset for Intel CPUs.