OP - you can't get that high on your P8P67 - roughly 2133 max.
Your going have to go z77 to take advantage of that speed.
People will say memory speed doesn't speed things that much - when compared to the cpu overclock, ssd, or gpu - it's definitely true.
However, when you're at the max levels for your cpu/ssd/gpu the memory is one of the few things left to tweak.
There is no giant gain, but perceptionwise your system will feel more responsive and snappier.
Otherwise everyone would be running the cheapest value ram ddr3 1333.
Going to 2133 from 1333, 1333 will feel like a stick in the mud.
You don't have to spend megabucks for ddr3 2400 either.
The $46.99 Samsung 30nm 8gb kit will do C11 2400.
The $59.99 G.Skill C11 2133 8gb kit will do c12 2400.