[tuxen]

Also it might be the USB sticks that I have but the transfer rates was basically half of the sd card.

What did you use to benchmark them? I've benched my SD and USB on my PC with CrystalDiskMark, so I know what they can achieve but the results might be quite different on the Pi.

Just a simple dd test. But yeah I know though writing a big file can be faster on sdcard things like scanning your library and getting metadata and other saves seems faster on USB it think this is due to the hardware though.
Read speed are the same so once the library and metadata is saved and with the difference overall for me between the sdcard's I have and the USB stick's I have and particular the no overclocking problems at all I prefer using both USB connectors for hard drives instead.
And if anything using a harddrive for the Storage partition which is much faster than any USB stick.