I was thinking of making it totally flat from the bumper lip in the front to the bumper lip in the rear. If I did that I could lower it maybe 1/2 inch lower than stock to make the control arms sit level with the pan. I would like it lower so if you think that going lower than that won't affect anything I will probably just use my chopped XFi springs.
I could angle the rear upwards some and just cut that rounded lower section off the bumper and just make it like a smooth roll pan on the back.
From that pic you can see the rounded part of the bottom of the bumper, if I cut that off that would give me a slight upwards angle on the rear of it.