Hi, I can't really help you much on GT3, not even got the game yet, But, with all my experience in GT & GT2, with some of the best Online Racing guys around on the internet. I can tell you they always, well nearly always, set the LSD settings all on 1, no traction control either, and they run very firm susspension settings.
See if that helps.
cya
PS It worked well on the FTO LM in GT2
(Edited by robisme at 11:51 pm on July 17, 2001)