ride quality on 18/20" wheels and coils

[68c10airstream]

Looking for feedback on 18/20" wheels on coil sprung c10's. I have a 68 c10 with 2 1/2" drop spindles with stock coils in front and 4" dropped coils in back, all from e.c.e. Considering 18x8 front 18x9 rear 55 aspect ratio tires, or 20x8 front 20x9 rear 45 aspect ratio. I've looked at times for opinions on ride quality and would like to go with 20's but hesitant as i think it will ride too firm. Going for a 28+" front tire diameter and a 29+" diameter rear tire using either a 18" rim or a 20" rim. I've decided on mobsteel steel wheels with a beauty ring and a poverty cap. Thanks in advance!