DDR 3-1600 Mhz on Motherboard supporting 1600Mhz OC only?

1. It means that the RAM speed will default to 1333 and you'll have to manually select either XMP or 1600 in the BIOS to get full RAM speed.
2. Yes, it will work at full capacity.
3. The board in that combo probably won't overclock the CPU to its fullest**. As long as you're okay with that, the combo is good.

**Why won't it overclock the CPU to its fullest? The power system on that board isn't the greatest for everclocking -- it needs more phases. Plus, the board doesn't have any heat sinks on the power system to keep those chips cool. There are definitely better overclocking boards out there, but they are more expensive.

Note that the power system on that board is perfectly good for stock speed and moderate overclocks.

Memory is sold by the fastest guaranteed speed that it will possibly run at, not THE speed your particular system will run it by default, the motherboard actually sets the speed, which will be 1333mhz. (or something even lower depending on the hardware configuration of the specific PC you are putting the memory in) To get 1600mhz memory, or any memory faster than that, to run at its max "rated" speed, you must manually set the memory speed. (overclock it)