I've now gotten 304 runs in, while I'm still working on this I doubt I'm going to get to 1000. Regardless, this is a little more precise now.

This is the basic rundown:

PART BONUSES:

Acceleration: 19.41%

Braking: 27.3%

Grip: 23.03%

Speed: 30.26%

PART LEVELS:

Level 50: 4.28%

Level 49: 2.3%

Level 48: 3.95%

Level 47: 2.63%

Level 46: 4.61%

Level 45: 4.28%

Level 44: 9.21%

Level 43: 11.84%

Level 42: 13.82%

Level 41: 25%

Level 40: 18.09%

All this data can bee seen on my spreadsheet, here:

https://docs.google.com/spreadsheets/d/1TbhANTSOZIGcuQG5uWVdPAVbhvBf79RRod9avMZym5s