Here's your spec sheet for your cpu:
http://www.cpu-world.com/CPUs/Bulldozer/AMD-FX-Series%20FX-9590.html
According to this, your supported memory: DDR3-1866
So I would recommend pursuing this or higher with of course the lowest cas frequencies. Higher speed is better than lower cas (2133 with higher cas is better than 1866 with lower cas). But 2133 with higher cas is obviously not better than 2133 (same speed) with lower cas.
That said, also make sure the memory is checked against your mobo for compatibility:
http://www.asus.com/Motherboards/CROSSHAIR_V_FORMULAZ/#support
Check this for extra peace of mind for compatibility or you may learn the hard way! Other than that you've done your homework and it's a matter of personal experience and opinion.
UPDATE: I took a moment to check the compatibility list and it was rather light. The only ram I found listed was this:
f3-2400c10q-16GTX(XMP). I tried seeing what I could find and this was the closest:
http://www.newegg.com/Product/Product.aspx?Item=N82E16820231590
It's 4x4GB sticks yielding your 16GB but not in the 2X8GB fashion you initially requested but I wanted to find something to help point you in the right direction along the lines of what you are asking. Not exact but close.
Now these are not on the compatibility list but are more inline with what you are asking:
http://www.newegg.com/Product/Product.aspx?Item=N82E16820231589
http://www.newegg.com/Product/Product.aspx?Item=N82E16820231623
In the reviews about a dozen people with the same board have had good experiences with the 2400 speed ram. 2 reviewers with the 1866.
Hope this helps! Have fun!
Thanks,
Justin S.