Are both compatible with mobos that support ddr3-1333?
Most RAM is backwards compatible (so long as it's DDR3), and if your running an Intel processor, then the memory is handles by the CPU. If I recall correctly, the i7 9xx CPU's limits the speed to 1066. I believe SB will run 1333Mhz ram at speed.
Now I maybe mistaken it but I had heard that the reason that they most of the memory manufacturers don't use the 666 is for fear of being labeled as the number of the beast and chasing away customers.