blazorthon :
... Also, XMP doesn't set RAM to 1600MHz unless it is supposed to because XMP is different for different modules. Some have it at 1866MHz or even 2133MHz. You might want to know that not all modules suport XMP...
Hehe, I guess I could have been more specific a little. I was referring to the OP stating that he has 1600 RAM that he is not sure how to get to read at 1600 RAM. Just pointing out the fact that if he has a motherboard that has XMP in the BIOS that if he enables it, it will (should) auto set his RAM to it's true tested speed (in this case 1600) and that is if the RAM has X.M.P enabled. It should say on the box you got or you can check the manufacturers site to see the exact specs.
@OP: Blazorthon is right though, your RAM has to support XMP as well as the motherboard. Otherwise the option will not be available. Manually overclocking the RAM is also possible. I do know that when setting the RAM to 1600 or above (whether manually or via XMP), it requires the voltage to go from 1.5v to 1.65v. (Most BIOS and motherboards nowadays does this automatically when you change the RAM BLCK). While it's not a huge change, it can be potentially harmful for both your RAM and CPU if not cooled properly etc. 1333MHz is the main standard. Anything higher is actually "overclocked" and as is the case with any overclocked module, it must be properly cooled etc. But it shouldn't be a big problem since most RAM modules these days come with pretty good heatsinks and CPU's generally don't get too much hotter with the RAM at a faster speed. As long as you leave it at the speed the RAM is actually meant to be at (in this case max 1600). Don't push it over it's manufacturing limits unless you really know what you are doing.
Personally though I would suggest leaving it on 1333MHz if it's just for gaming. You won't see a difference. If you are using rendering and/or compression software a lot though, you will see a difference and will be happy with the results.