Since your running a one-way, I would assume that the car is most likely scrubbing speed because the rear is too tight. But it could still be a combination of the front and rear though.
The first thing I would recommend is to make sure your rear diff is running very smooth and that it is as loose as possible. Here is a post where I explain how to set the rear diff:
http://www.teamxray.com/xforum/viewtopi ... 3909#23909
From what I see in your setup, I would then try the following:
1. Raise front downstop to 1
2. Use light blue springs in the rear
3. Change to low rear diff height position
4. Close one hole on all four shocks
5. Change to violet/blue fr/rr spring combination and move their upper mount positions in one hole to #3/#4. This should somewhat maintain the initial spring stiffness of the softer springs, but they will progressively stiffen quicker and not allow the chassis to roll as much.