Disk Drive Controller
The system drive controller is an important part of system performance. In most modern boards your drive controller will run off of the PCI-e bus. The PCI-e bus performance can be affected by poor trace layout as well as many other design choices that show up on different boards.
For testing we use Sisoft's Sandra and Everest.
Here we find a rather disturbing trend. The HDD speed found on the P55 Extreme4 is not as good as what we saw on the 870 Extreme3. It also drops off somewhat during our overclocking testing. This is a little bothersome and something certainly to be aware of.
Everest backs up our findings with Sandra, including the tendency to drop in performance when overclocked.