The maximum memory speed listed in the processor specification is the maximum speed that Intel validates and thus will guarantee. This does not mean that higher speeds will not work - with a good quality motherboard and good quality DIMMs, they might work just fine - just that they are not guaranteed to work at this speed. Note the following:
The issue is noise. The processor, the motherboard and the DIMMs all generate some amount of noise and each contributes to the overall noise level. Motherboards are designed to limit noise, especially that from secondary sources. If the overall noise level exceeds the processor's ability to reliably distinguish data bits from this noise, memory reads will fail. As components age, they generate more noise. This means that, over time, combinations that worked initially may not continue to do so.
A secondary issue is the fact that, while running the memory controllers at speeds above their guaranteed levels, they generate more heat and this heat will contribute to the package levels that need to be handled by the cooling (fan speed control) subsystem. Technically, running the memory controllers at speeds above the guaranteed levels could be considered to be a form of overclocking.
Lots to think about.
Hope this helps,