Interestingly I did a test on some harsh washboard yesterday with some 32mm tires on my Inflite
At 15-16mph the canyon carbon seat post just soaked up the harshest washboard. I didn't realize how hard I was punishing it until I put my weight forward gripped the handlebars - the front of the bike was getting the cr*p violently beat out of it. I quickly put my weight back on my saddle with a light touch on the bars.
I don't know how much was the bike and how much was the seat post, but dang, the back of this setup soaks up bumps. I do think that at speeds closer to 20mph+ that the bike would just violently skip across the tops of the crest of the washboard, but I haven't had a need to use the thudbuster since getting this bike/seatpost combination.