Just to complement the information.
I use clover on a H87M-D3H board, and have windows 7 and mavericks installed.
XHCI is the intel USB 3.0 controller and means how it will route the USB ports. If you enable it and also enable all the Hand Off options, Intel driver (on Mavericks and Windows) will route the USB ports like this:
All devices plugged on USB 2.0 ports will operate at USB 2.0 by the intel XHCI driver (mac inclusive)
All devices plugged on USB 3.0 ports will operate at USB 3.0 if they are compatible, if not it will operate at USB 2.0 by the same XHCI driver.
All other options (XHCI and Hand off) will change this behavior allowing more compatible routes but unfortunately some USB 3.0 devices will operate at 2.0 speeds because some routes has 2.0 devices plugged and will be routed to an old EHCI driver (route = hubs and devices plugged in a chain...)
In my case, my monitor U2713H has USB 3.0 ports and USB 3.0 Card Reader and I plugged an apple keyboard (who has a internal usb 2.0 hub with 2 ports and a IOGEAR bluetooth plugged under the keyboard) and a Transcend USB 3.0 card reader (because this one has compact flash port). So I have an USB 3.0 cable from the monitor to USB 3.0 port on my motherboard and a mix of 3.0 and 2.0 devices plugged.
In all modes but XHCI enabled and hand off enabled the route was transformed to a USB 2.0 speed or one of the card readers (the Realtek inside de monitor) became 2.0
The same behavior happens on Windows 7. So, it is not a Mavericks or Clover behavior, but a hardware definition.
Unfortunately, in XHCI enabled and Hand Off enable all devices works but the iogear bluetooth won't pair any devices. It seems a failed compatibility product, because other bluetooth dongles, like a generic broadcom 2.1 I also have, works ok . The iogear only pair if it plugged on a USB 2.0 native port AND XHCI in auto or manual (routing all USB 2.0 port to EHCI driver but not the XHCI intel driver). Even in Windows...
Also, i burn one of the iogear trying to work directly on a USB 3.0 port, expecting it works on 2.0 compatible mode, but it become hotter and hotter until it burn. I have another one to try and it have the same behavior (I plug off before the second one burn... of course). All the other usb devices i have works fine on Usb 3.0
I will try to find another bluetooth 4.0 dongle with broadcom chipset that will have compatibility with USB 3.0 at least intel and apple have another driver to deal with this problem.
BTW, intel launch another USB 3.0 driver for windows, but i can't install until gigabyte have another BIOS (i use F6, the last one). The driver crash every time i try to install, and I research all other motherboard makers (asus, etc) and all of them has a note to use the older version of USB 3.0 intel driver. It seems the new driver require a new bios. we need to have patience until they are available....
and intel has now two USB 3.0 drivers, one exclusively to series 8 boards and other for all older series boards. it seems the USB bug on haswell chipset (first stepping) is more severe that we think...