I would say maybe the issue is not just "USB3", but some other bottleneck. Personally I have not use any usb3 so I can't say if that's normal but I have used sata vs usb2 and sata was definitely faster (my experience).
Just thinking out loud, maybe a new usb3 controller if you have the socket for it (I notice they are not that expensive).
Data transfer speeds via USB port are very different. It certainly related on system settings (win7_64bit) as well as file type, USB2/3, etc.
My question is related to USB3 transfer, which should be the fastest, but sometimes it's frustratingly slow. I tried several new USB3 external hdds (WDpassport edge 500GB, Adata HV620_500), various flash memory. At the beginning of the big file transfer (1GB), it sets off in cca90MB/sec, then it slows down to 4KB/s. It's somehow improve? Update drivers, or something? I use both Windows Explorer or Total Commander, it's the same.
Thanks for your advice or tip for acceleration.