For gaming, higher speed generally shows better results.
I'm not sure what's happening but you should easily be able to run one stick at 3200MHz.
What I will suggest next is resetting to defaults and entering the Voltage, Frequency and Primary Timings manually.
Enter the bios and reset to defaults (F5) and set...
Dram Frequency - 3200MHz
Dram voltage - 1.45v
CPU Sytem Agent voltage - 1.25v
CPU VCCIO voltage - 1.25v
Dram Timing Control - At the very top, enter the primary timings
16
18
38
Command Rate - 2T or 2N
F10 and Enter to save and exit.
How does it go setting the ram manually?