Maybe this is rehashing an old thread from before I joined the list, but back in the '70's I'd heard that 4x or tangential spoking made for a softer ride, and that low flange hubs also made for a softer ride. Conversely 3x, high flange wheels were the strongest and stiffer wheels. At the time, I'd also heard that 2x was not quite as safe a wheel and that radial spoking wasn't laterally very strong. I'm not sure how true the last sentence is with no practical experience. And now, box section rims are supposed to be more supple than aero rims, which seems like common sense.
My Richard Sachs was built to be a stiff, fast tourer, and as such has helped me to notice the subtle differences in wheel stiffness. I started out with low flange 4x for the reasons above, but after destroying the rear rim with a pothole and steep hill combination, I rebuilt the wheels 3x because I didn't want to wait for spokes to come in and the guy I bought them from assured me that I was blowing smoke and that I wouln't notice the difference. The ride was noticeably stiffer transmitting road shock on rough roads to the handlebars and seat. I lasted almost a month before rebuilding the wheels 4x.