A 1 in 12 is best for 55gr and under, you might manage to do well with 62gr bullets in a 20in if the velocity is good enough.
A 1 in 9 is good for up to 69gr in a 20in barrel and maybe even in a 16in... And 1 in 7 can handle up to around 80gr well from a 16in barrel.
1 in 8 can do up around 75gr in a 16in barrel.
Your results may vary, as these are just rough guidelines.