Windows 8 has animations for both the start screen and the login screen. These occur when the start screen is loaded and the tiles animate in. The same thing happens on the login screen where the available users animates in. These animations cause quite a bit of lag over Remote Desktop as it tries to send each individual frame of animation. Is it possible to disable these animations?
This is probably what you need: http://www.howtogeek.com/128306/how-to-disable-the-animations-on-the-windows-8-start-screen/