The speed that you are getting when transfering you files via your PC is probably the max, since you are limited to the transfer speed of the connection between you PC & the HUB.
When you use the sync, you are using the direct connection speed, but when you transfering files using your PC you are basicly transfering the files from your external HDD to the PC then back to the HUB. So what ever transfer speed you have when you transfer fles from your PC to the HUB will be the same if you transfer from your external HDD to the HUB via the PC.
About the only way to get a faster transfer is to either upgrade you wireless or go wired. I have a combo N+ router (it has both wired & wireless) & wired it get’s about 8Mb/sec from the PC to the HUB.
