I run a Calsonic at an online league. It isn't the most powerful of the GT-Rs, so you'll need every bit of speed you can get out of it. Try keeping the default settings, but lowering the car height to front -5 and rear -10. The lower body will give you more grip at the corners and the lower rear increases top speed.
Hope this is helpful, but you'd be better off with the Xanavi or Motul GT-R's. I don't now why, but the Xanavi's engine revs at 12.000rpm while the Calsonic's stops at 9.000rpm...that makes a huge impact in lap times - around 1 sec in a fast track like monza...