20" spring question

What would yall think would be a good starting point for rear spring rates on the rear.
Ive always ran like a rf1000 lf900 rr200 lr250 with 11in springs on a Metric. Really wanting to try the 20" springs in the slick. Thanks yall

Oh and are stock spring mounts on the frame still used? Not like IMCA street cars with the bar and jackbolts?

all gonna depend on where you've got your weight, driving style etc. best way to do it is to just put the 20" spring in and try it. might have to go up one spring on your rr. you gonna mount the spring on top or in front of the axle on the lr?