Problem is your hard dirve write speed. Each hard drive can only process data
as fast as its technology will allow.

Using a SSD or Flash Drive may increase your website copy speed.

Using the drive for example that your PC has its System files saved too will
be limited greatly on the speed or read/write actions, since usually this
drive isn't designed to process large data quickly.

Using an additional or external SSD drive should increase your overall
download speed above that of a Flash Drive (which may be used in the event of
only option and still probably faster than your System drive.

Least my Website Copy speed increased over 60% after switching to a high
quality SSD drive.