the problem I see is that you are using a Negative Speed with Direction.
What does a negative speed mean to you…going backwards? This is being taking care of in the direction component of the graph.
I suggest you design for speed 0 to 600 only. Move the zero line down to the bottom and layout your blendspace differently. Here is an example of a 9 way blend, you could omit the NW,NE,SW,SE and still get good animation. =)
