I would like to share with you a very similar conversation I had on this same subject; https://communities.intel.com/thread/108512. I believe this conversation answers your inquiry, please check and of course if you have more questions in regard to this memory issue I will answer them.
There is some good information (mine) in that other conversation, but, unfortunately, Amy is incorrect in one of her answers...
First of all, when you install 2400MHz memory, the BIOS is going to try to run it at 2400MHz. No, it does NOT default to 2133MHz. Only if the memory fails to work at the SPD-specified speed (indicated by seeing POST error message), will it fall back to a 2133MHz default/recovery configuration and try to run with that.
Intel designs for and warrants operation at 2133MHz. Any higher clock speed is considered overclocking and Intel officially does not support overclocking. Now, this does not mean that your system, with 2400MHz memory installed, is not going to work. In fact, in many cases, it will work just great. What is does mean, however, is that, if it doesn't work, Intel won't be held responsible.
Here's the issue: If Intel does not specifically design for faster memory speeds, things could go awry. Worse, it could work perfectly for some period of time and then start failing. From a technical standpoint, the issue is noise. Many parts of the system generate noise that could affect the operation of the memory busses. The processor's memory controllers, the bus support circuitry, the DIMM sockets, the DIMMs themselves and the memory ICs on the DIMMs make up the set of components that most-directly contribute to the noise levels on the (two) memory buses (but other components - including some outside the chassis - can still affect it). For a particular board, with a particular DIMM or pair of DIMMs installed, the noise level on the busses will allow effective data transmission on the busses to some particular maximum (MHz) speed. Intel designs for and guarantees that this will be at least 2133MHz, but no higher. It is possible - and indeed likely - that operation at higher speeds will be ok. In fact, I have heard from one user who is using 3000MHz memory without issue.
As I said, it could work perfectly at 2400MHz for some period of time and then start failing. Why? Well, as components age, additional noise can (and will) be generated. This means that, as time goes on, the maximum effectively-supported memory bus speeds will be slowly dropping. Intel guarantees that it will stay above 2133MHz over its entire warranted lifetime, but they do not warrant, for example, that it will stay above 2400MHz. Thus, after some period of time, this 2400MHz memory could appear to fail. Further, how well the overall solution works is also dependent upon the quality of the DIMMs being used. Unfortunately, I have seen 2133MHz DIMMs that don't work even at 2133MHz. For this reason, I stick to name brands and I stick to 2133MHz DIMMs.You get what you pay for.
As I said in that other thread, using faster DIMMs does not necessarily result in a faster system. The amount of memory installed makes *significantly* more difference to the overall performance of the system than does the speed of the memory...
I hope this explains it well enough...