I have run it in front, middle and the rear-most positions and I feel the front position makes the body perform with less sidebite, especially at lower speeds (not super low though). At high speeds the overall shape of the body seems to provide most of the performance dynamics. Moving rearward makes it slightly more stable... but this change is a very slight one.
If you usually have more than one body on hand... make one wing with the forward-most and rearward-most holes on one wing and the middle hole on another. You can just switch them out to see the changes it makes. Oh yeah, I use the forward most position because of my really tight track is filled with 180 degree turns every race.
Just my opinion on the matter.
*just about any change you can do will make more of a difference than the position of the wing. It is not much, but I like it*