The problem is that the RAM is designed to run at a speed of 1600 whilst the motherboard only supports 1333.
How big a problem is this? will the RAM damage the motherboard? will it refuse to start up? Or will it simply lower the memory clock speed? Do I need to cancel the order immediately? Will I have to mess with the BIOS?
YES I did but i have never built a system before and wasn't sure that if I built this system if it would even start up, don't you have to be in the BIOS to OC?
Yes, but you won't even be able to tell the difference between 1333 and 1600 unless you run benchmarks. If you don't do anything, they should run at 1333.