The speed of the character has not been sped up in any way. The running speed is exactly the same, the reason we are thinking it is faster is because of graphical illusions.
Two things are contributing to this.
1.) Lighting and sharper shadows.
2.) Lack of any upper body movement in the character compared to GRAW 1. I personally compared it last night with testing. In GRAW 1 there is a signiffigant amount of bouncing and upper body wobble when running. This creates the illusion of weight and as if you are lugging around. So when the lack of movement and complete stiffness of the upper body id applied in GRAW 2, it takes away the heavy illusion and replaces it with a quicker sense of speed.
Now whether there is a framerate problem or whether its lag causing the "skipping" so many are reporting will have to be determined in the retail version.