M21 and M22 had the same gear ratios. Low was 2.20. M20 had two different ratios, but they were close: 2.53 and 2.56.

With a strong engine, I prefer the M22, as the 20 degree gear angle and higher nickel content made a much stronger box. With a little weaker engine, the higher low gear gave a little more kick off of the line.

Although, I ran an M20 in a 68 GTO in the 11's and never broke it. After about 8 years, I took it down and replaced the bearings and synchros. Ran it another 8 years.