Auto timings are designed to work "on every box". If you're not stable at 'stock" settings" something is wrong with your build or your windows install.
CAS 7 means it waits less time between doing things than it would at CAS 8 and more time than at CAS6
12 GB is an extraordinary amount of memory for a windows based system unless you are doing 3 D modeling or something real demanding. FWIW, I haven't had a MoBo BIOS correctly pick up my RAM's timings in at least 4 years.
I'd:
1. Put in just 3 modules, look in mobo manual for correct slots to use.
2. Set BIOS to all defaults
3. Set memory CAS timings to what "it says on da box"....i.e. 7-7-7-20 or whatever is on the label.
4. Save BIOS settings.
5. Run memtest+ 4.0 (www.memtest.org) at stock settings [BCLK = Auto / Mem Multiplier = 8 / BCLK = Auto (133)]
6. Set CPU mutliplier to 12, set mem multiplier to 10 (1600), set BCLK to 160 (this will test RAM at 1600 and insure CPU don't mess w/ test)
7. Save BIOS settings
8. Run memtest+ again.
9. Swap memory modules and repeat steps 5-9 (check that you still have correct timings)
10. Stick in all 12 GB, repeat steps 5-9
If you pass this, you have eliminated memory as the issue. Gonna take a few days as each memtest should run 8 -12 hours.
Contact RMm manufacturer for advice while you are waiting.
Voltage is to be "played with" only once you have stable system. You can drop Vcore bit by bit until system becomes unstable. I got down to about 1.05 volts but as it offered no temp reduction, I stayed with 1.125