As far as gearing goes....
Silver can: I was running somewhere in the low 5's (This can obviously change based on the size of track, ours was decent, with flowing corners.
17.5: This one is more based on temp than anything, currently I am in the 3.7 range. (86x50 to be exact, keeps me right up with the fast guys.)
As far as bodies go, at the TCS in Cali, the popular body was obviously the NSX, But I talked to a few guys and they also like the Corolla Axio as well, this will be what I run for our TCS in Wa.
I currently run a gear diff in the rear and a spool up front, I love the predictability of the car with this setup. The rear diff currently has 3k oil, the car really rolls well through the corners.
I currently run the IFS, but will be trying the standard front end for the next race. I really feel like you should give the IFS a chance, mine handled great, and had no issues. The one thing I would suggest with the IFS is to buy the Alum. rocker arm set. That will take out all the slop, which is critical on IFS cars.
Hope this helps! I absolutely LOVE my 06 so far, running a TCS spec car against 600 dollar cars and competing is so much fun
