Google is your friend my brother...
Honestly, the frequency difference is comparable to cas difference. If you're between CAS 9 1600 and CAS 11 1866, it's basically the same deal when you get down to the basics. Keep in mind the 266mhz difference in transfer speed can be canceled out by a faster access cycle from the RAM. CAS is measured in nanoseconds and transfer speed is measured in hertz/seconds.
Honestly, with the price differential on some RAM sets, I don't find the extra cost is worth the bonus. Just invest in some nice 1600 CAS 8 or 9 RAM and you'll be a happy camper. Also, if you're using an AMD chip, keep in mind the 8350 can only handle 2 modules of 1866 on one motherboard, basically leaving you with only 16gb for the rest of the life-span of your computer. If you're using Intel chips, I believe the memory controller is a little more lenient, allowing 4 sticks of 1866 but doesn't go any higher.