Thanks for the replay, nikorr! I should have clarrified that I am using a Corsair Survivor which has the following specs:
80 MB/s sequential read — 40 MB/s sequential write
When writing to my Corsair M4, which has write speeds of well over 200 mbps, I am only getting ~30 mbps. This speed is achieved using 1 large ISO file. On top of that, ASRock has USB 3.0 "turbo boost", which is supposed to increase speeds. I have tried with this program running and turned off. Both yeild the same speeds.
I have also updated to BIOS 1.36A, which is the lastest ASRock BIOS.