The results would appear to be no change, or too small to notice in tank averages.
Update: The spoiler is off, and replaced with trip wires to give the air a clean edge to separate from. Soon I'll be attaching the side supports I had for the kammback to give a vertical surface off the cabin to reduce vortex generation.
The spoiler appeared to produce some downforce. The bottom of the center support was actually bent inwards.
I took a look at the end of the roof and it's slope, and the glass is somewhat inset. The angle before the separation hits the trunk about an inch or two before the edge of the trunk.
