In our case, using ASUS Z97-USB 3.1 series MOBOs and observing slow and slowing USB 3.0 file transfers, we found that reinstalling the USB Driver set (eHCI, xHCI), along with the Intel Rapid Storage driver, all found on the ASUS driver install CD, corrected our speed issues quite satisfactorily. We confirmed this on two separate devices that were built up independently, fully configured with Win7 Enterprise x64. Our SAT routines (site acceptance test) now include a USB 3.0 throughput verification and driver re-install if necessary. Our file transfer test was a 24GB file moving from onboard SATA HDD to external USB 3.0 HDD - the process improved from 45+mins to 3.5 mins.