This was posted from many users and some sites, but Techspot made some tests and the results are... stunning!
Memory Performance & Wrap Up
When benchmarking the Intel Haswell processors, the memory speed in the BIOS kept reverting back to 1333MHz (was an issue with the BIOS which has now been fixed) at every processor change rather than holding the DDR3-2400 XMP (Extreme Memory Profile). At first we accidently tested the Core i7-4770K with the memory clocked at 1333MHz and were perplexed by the much weaker than expected performance.
It was quickly spotted that the memory was running much slower than it ought to be, though we weren't entirely sure this was the cause of the massive deficit. Turns out it was, as moving the memory back up to 2400MHz resulted in a massive 67% increase in minimum frame rate for the Core i7-4770K.
A similar situation was found with the Core i3-4360, which went from a minimum of 41fps with DDR3-1333 memory to a minimum of 65fps with DDR3-2400.
Yes, we know there's a significant difference between the now obsolete 1333MHz memory speed and 2400MHz, but from memory I don't recall it having anything like that kind of impact on gaming performance. Interestingly the same variation in memory speeds had little impact on the AMD FX-8350's performance, as the processor was just 13% faster with the quicker memory.
Anyway, we found this interesting and it would suggest that Fallout 4 fans with Intel hardware will want to ensure they are running their memory as fast possible.