Use this gear ratio calculator to figure out your max speeds for each gear using whichever final ratio you choose. Make sure to use either the correct Manual or automatic gearing ratios. And change the tire size to match yours.
E86Z4 3.0si / M Coupe Manual
I: 4.35 II: 2.50 III: 1.66 IV: 1.23 V: 1.00 VI: 0.85 Reverse: 3.93
Final Drive: 3.46:1
Redline: si 7,000 / M 8000
E86Z4 3.0si / 3.0i Coupe Auto
I: 4.17 II: 2.34 III: 1.52 IV: 1.14 V: 0.87 VI: 0.69VII: -Reverse: 3.40
Final Drive: 3.64:1 / 3.73:1
Redline: 7,000
https://web.archive.org/web/20200729...calculator.htm