I have the voltex on mine, i have it set pretty much flat so i am getting some downforce just not as much as i could do if i angle it down more. Through turn 1 @ harris hill where you are going full throttle i really felt a difference in how planted the car feels now, it just gives me much more stability and confidence. My last two mods were going from track pads, fluid, and lines to the AP Sprint kit with race pads and the voltex wing. This helped me shave my time from a 1:31.3 to a 1:29.8 i think the mods in conjunction worked very well. Dont know if the downforce of the stock wing will be the same, but i would like to share my experience that i had while adding rear aero.
You can see the angle in this pic:
