Funny how any thread related to a difference between 2D and 3D always turns into one where folks tell us why one or the other sucks and the other is better and everyone should use it...

Anyhoo, from what I've seen it depends on your system. If your 'puter can handle it, 3D isn't any laggier than 2D really - the difference is in the animation. 3D might appear slower to you because of the way the running animation is done, the steps just seem longer and thus slower whereas in 2D the chars just sprint immediately so to speak. The speed of the actual movement is the same however.