Good to see someone trying out new things for LFS screenshot editing.
What you need to do for a quality motion blur though is take two screens from the same position in the same moment: one with and one without visible car. That way you can blur the background picture, cut out the background in the picture with visible car, make them overlapping layers et voilà, no blurred edges.
I like all of them except for the fourth. It looks like the car is going 400 km/h but wheels almost lock up. Wheel blur should exceed motion blur. Oh and the smoke/dust looks weird. :P