It only officially supports those speeds. However, P67/Z68 boards also offer 1600, 1866, and 2133 RAM speeds in the BIOS. Those settings work just fine, as long as the RAM itself will run at the selected speed.
If you buy 1600 or 1866 or 2133 RAM, you can change the BIOS settings to run it at full speed, yes. It is still compatible with the CPU at those speeds. I know this because I run 1600 memory at its full speed in my Sandy Bridge system.
If you mean taking 1600 RAM and trying to run it at 1866, it might work but it's not guaranteed.
I prefer the 1600 DDR3, not so much for performance as it is only a couple of percent higher. I prefer it because I can run in synchronous mode. There is very little cost difference anyways. As to CL9, again Leaps-from-Shadows is correct that CL9 is very close to CL7 in performance. I use CL7 – but that is me.
Setting up the timings should be a piece of cake. Just go into Bios and select XMP (probably profile 1). Bios will read what is stored on the RAM chips and set everything accordingly. On older systems this was kind of hit or miss, but newer systems seem to have made it more bullet proof.