I was working on some calculations yesterday around latency and different types of storage. Using some 'typical' figures you would see SATA being around 40 milliseconds of latency, SAS would be in the region of 20 milliseconds and PCIe around 50 microseconds. You can tweak the speed that data comes back but you still have that basic latency. This is something you have to add to every single request to get data back from the disks.
Every touch point in the setup has the potential for latency and also the potential for failure. Network card, cable, switch and so on until you finally get to a disk that has to revolve (and you wait your turn with other requests). The beauty of systems like FusionIO is that it removes these failure / latency points, gives you a massive performance lift and allows you to have a less complex system overall while reducing costs.
If you had the same schema design, data and queries and did a direct comparison between the three you will see a clear performance winner. The complexity gets reduced significantly as does the failure points and latency.
Having the right design makes the world of difference but no matter what we do if there is an underlying latency you will not remove it by schema design.