Slow file transfer with Windows file sharing

"The percents you're seeing relate to the network card in the computer, and not to the speed of the network itself, which in your case is dictated by the router.
I would guess that one of the machines has a network card rated at 100MB and the other at 1GB.

Also, the displayed percentage is just an approximation that might be off the real value by dozens of percents, so just take it as an indication, rather than precision science."