The Crosshair IV Formula board supports 1600, 1800, 2000. The thing is, you're going to need to force the ram to run at these speeds.
What this means is that the motherboard will not auto-detect timings for DDR3 1600, 1800, or 2000. The reason for this is that the timings and voltage vary so wildly at those speeds that it would have caused more problems to try and generalize the memory and run it at any particular timing.
Your motherboard is loading the JEDEC specs, which is the standard for memory specs. JEDEC issues specifications for various speeds of memory so that when you turn it on the computer actually comes on.
The EPP specs are what you want to run, but they will not be automatic. You have to make the ram run at that speed.
You should reduce the timings to whatever they were advertised, and try to push the memory farther in the BIOS. This can be done by simply increasing the multiplier, decreasing the divider, or increasing the FSB.
That Asus motherboard of yours has all of the features +++++ that you'll need for the job.