Don't tear your hair out. Use the Mine's Skyline and you will beat it quite easily. You already should have it for S-4 (iirc)
Well I managed to get 3 with a slight variation of your tune.
I changed power to -15 . Weight to 85, and downforce 20 - 35.
And i finally passed it.
I could even had golded but I got a colison penalty once because the AI rammed into me when I was breaking for the hairpin, also got slighty off track once. with out those two mistakes it would been gold i think. But anyway im happy I passed the test.
Thanks for your help