Make sure that airflow is going over the VRM heatsinks,and mount a fan on the back of the board to cool the VRM's extra. It definately helps to maintain stability under load.
Make sure that all extra power sockets are populated. The 8-pin, 4-pin, both at the top of the board. And the molex 4 pin socket, middle/left side of the board.
Make sure the 'slow mode' button is set to 'off' (and LN2 jumper also)...Top right side of board.
Enter BIOS and hit F5 to revert to default settings. Set it up like this;and don't touch any other voltages and/or power saving settings.
Disable AMD Turbo Core Technology
Load Line Calibration: Regular (yes, the 9590 @ 4.7 is stable at this lowest setting)
Current Capability: 100%
CPU Power Phase Control: Extreme
Switching Frequency: Manual
VRM FFM: 300
CPU Power Duty Control: Extreme
CPU Power Response: Medium
[Advanced->North Bridge->Memory configuration]
[Tool->Asus SPD information]
Take note of the profile you want to run your memory at. Write down first seven values,and the last one (CR)
Manually choose the memory frequency.
Enter the Dram voltage that goes with the profile. (more towards bottom of page)
[Dram Timing Control]
Manually enter the first four timings,and at the bottom set the Command Rate.
Don't change any other frequencies or voltages.
Thoroughly test your system, like 24h of IBT on Maximum.
If it succeeds, store a profile in your BIOS profile page and call it 'stable'
Move on from here if you want to make any other changes in BIOS. Repeat the stress test after changing stuff! Should it fail, revert to your 'stable' profile.