I bought my x6 during the winter here in canada and went to a hard buttery clay track in the US for one meet. I found that the rear was loose.
for the beginning of our season here at sid's raceway,
www.sidsraceway.com, I also found that the rear was loose.
just recently my line has improved with my setup as well and to prove it my results have gotten much better. I used to have it tough getting into the a main however at this past race, I qualified 5th out of about 30 drivers.
I find that you can't underestimate the effect of the wing. it really needs to be cut right for the day's track surface, and it needs to be in the right position. I saw someone with the wing mounts in front of the shock tower and I think that it could be a great thing. worth checking out.
good luck
S