What's faster than a mirror driver in Remote Control Software?

I've done some testing comparing RealVNC enterprise (which includes a mirror driver) and Remote Desktop and the later is significantly faster than RealVNC with the mirror driver.

From what I've read before testing RealVNC, I was under the impression that the mirror driver would create a almost lag-free experience, but that was not what I found. Remote Desktop even allows you to display the full aero glass when viewing the remote desktop.

I've done my testing on a Gigabit network, with both computers connected via Ethernet.