Going from 32mm to 40mm tires has a speed penalty. Wider tires would do better offroad, but if one is only concerned with broken pavement, the Redshift stem provides vibration reduction without affecting speed.
I always toured on 35mm tires as a balanced choice, but recently I'm gravitating more toward 32s for road touring.
For a gravel tour, I wouldn't bother with the stem. Large tires are fine, as stated by others.
Last edited by Yan; 11-22-23 at 09:20 AM.