What drawbacks are there when using memory that is faster than what is rated by the motherboard?

Solution 1:

The 1600 MHz limit is generally imposed by the CPU, not the motherboard.¹Most motherboards support higher clocks.

If your motherboard supports clocks higher than 1600 MHz, you'll be able to overclock the CPU's memory bus. This usually goes well. I'm using 1866 MHz RAM myself with no instability whatsever.

If your motherboard doesn't support clocks higher than 1600 MHz, any memory you install will simply not be able to run at higher speeds.

¹ Traditionally, the opposite was true, as the memory controller was part of the northbridge (motherboard). However, Core i7 processors have the memory controller inside the CPU.

Solution 2:

The memory will run at the rate specified by the motherboard. Memory kits are sold at higher values to enable overclocking of the memory. Running this memory at a lower rate causes no drawbacks.

It's like running your Ferrari at normal highway speeds it can go a lot faster but its not harming the car.