1M 6-speed
1st: 4.110:1
2nd: 2.315:1
3rd: 1.542:1
4th: 1.179:1
5th: 1.000:1
6th: 0.846:1
Final Drive: 3.154:1
135i 6-speed
1st: 4.11:1
2nd: 2.32:1
3rd: 1.54:1
4th: 1.18:1
5th: 1.000:1
6th: 0.85:1
Final Drive: 3.08:1
M3 6-speed
1st: 4.055:1
2nd: 2.369:1
3rd: 1.582:1
4th: 1.192:1
5th: 1.000:1
6th: 0.872:1
Final Drive: 3.846:1
M3 DCT
1st: 4.780:1
2nd: 2.933:1
3rd: 2.153:1
4th: 1.678:1
5th: 1.390:1
6th: 1.203:1
7th: 1.000:1
Final drive: 3.154:1
So the final drive came from the E9x M3 DCT final drive (same ratio) but the transmission ratios, and likely therefore the gearbox, are straight out of the 135i. That should answer some questions!
JD