Interesting. One question: With what devices did you try to measure the speed?
For the software side I used the following apps to measure speed (i would be happy to use any suggested though):
Aja System test
Black Magic Disk Speed Test
The hardware side of things was done by using the the integrated USB 3.0 ports and:
Touro USB 3.0 500Gb external drive
SanDisk 32GB Cruzer Ultra USB 3.0 Flash Drive
I am aware I will get varied read and write speeds, but the results I get are below what I would get with ML installed or if I used USB 2.0 ports. I get write speeds on my USB 3.0 below 20MB/s and read speeds above 80MB/s with Mavericks. I have a test Drive with Mountain lion 10.8.5 installed on the same system and get Write speeds on my USB 3.0 ports above 160MB/s with the same hardware and bios settings when selecting that test Drive at boot. As soon as I upgrade the test Drive system to Mavericks I lose those write speeds.
I realize this problem is not a big deal for most but figured I would throw the info out there as there has been a lot of work done on getting USB 3.0 to work and even updating it for Mavericks specifically.