If it shows as 1600MHz in the BIOS then I would think it's running at 1600MHz.
What does MEMTEST say? ( www.memtest.org )
(You should run Memtest to test your RAM anyway OR you can also run the Windows 7 tool, Google or run HELP to figure that out. Start the memory diagnostic in Win7 and reboot).
- update BIOS if needed
- XMP profile, as mentioned (verify both frequency AND proper timings)
Bumping Voltage will not change DRAM frequency, you need to manually set DRAM frequency in BIOS/EFI. You purchased qualified hardware, so all you need to do is enable XMP profile and everything should be ready to go.
Here is a link to give you an idea of how/where to do it: