Further to the above, I am not a racer or fashion cyclist and think of myself as a comfort tourer. Speed and weight are not an issue. I prefer to get there eventually without sore hands, arms and back. The roads less travelled with sinkplatte are now not an issue.
There is no noticeable bob or sway when in the saddle with the seatpost. I am so used to it so can't say for sure but if there is, it is the least of my worries. This, with a Brooks is the best way for me to spend 10hrs daily in the saddle.
The stem is also a whizz. I have it fitted to a Jones bar so I have the best of both worlds. If I use a handlebar bag I use a harder elastomer.
Both these items have stood me in good stead and recommend them both, very highly.
As mentioned, I am not fussed about the weight of these two items when I have other stuff on the bike. Comfort wins every time, all the time.