SSD to USB 3.0 speeds

Just wondering if somebody can give me an idea of what kind of speeds I should be getting transferring a single 5GB file from a USB 3.0 external drive to an internal SSD (OCZ Vector 150) on an AM3+ board in windows 8.1. I'm getting a pretty consistent average of about 50MB/s and it seems as though that's about what I was getting before the SSD with an internal SATA III 6/Gbps HDD. Shouldn't my speeds have increased or is the USB device the limiting factor in both equations. Thanks.
 
So, even though I've still got a USB 3.0 drive in the equation, shouldn't I see some kind of improvement in speeds due to the SSD upgrade or no? Seems like even transferring files via copy within the SSD itself is about the same speed as the HDD was. And I've made sure the AMD SATA controller drivers are the most recent and AHCI is enabled. All drivers on the entire rig are current. That can't really be possible to have equivalent speeds on the hard drive itself unless something is wrong, right?