First off, the hard drive bays in the Mac Pro run at SATA 3, this is half the speed of SATA 6 and effectively cuts the speed of an SSD that can read at 550mbs to about 300mbs. If you have a later SATA 6 SSD that can read at 400-600mbs buying a PCIe SSD adaptor will speed up your drives; PCIe runs at the system bus speed of around 6Gps. They go for less than $100, usually around $30.

There are new SSD types on the market, OEM sales for the most part but a few companies offer them to us regular users. The M.2 PCIe format breaks the SATA 6 bottleneck of around 600mbs and companies like RAM City are claiming speeds of over 1000mbs for Mac pros!
So roughly 3 times faster than using an SSD in a hard drive slot.
Scroll to the bottom of this page where the comparisons are.

https://www.ramcity.com.au/buy/samsung- ... HCGL-00000
To top that off, there is a new type of M.2 on the market available from a US based company that goes to around 1600mbs!


http://www.anandtech.com/show/8236/sams ... me-support
http://forums.evga.com/Samsung-SM951-Av ... 61684.aspx
Looking like it's seriously out of stock, but the specs are pretty insane.
