The side to side rocking is indeed diminished when the ICE is one due to the gyroscopic effect it would have on any lateral movements. As for feeling it when driving on the highway at 60, just do what I do, use 'Rain-X' When I do, i will rarely need to run the wipers at all, as the Rain-X keep the front window very clean when moving down the highway.
This pretty common on Toyota's or Lexus. I had a 07 ES 350 that did the same thing when the wipers were on high.
Hmmm, I'll have to try the high setting. I use RainX on my windshield so I rarely have to have them on constant low. I almost always use the intermitent setting no matter hard it's pouring because the water just beads up and flies off.
I have experienced this many times since we have heavy rain here. I just imagine it rocks with the rhythm of the music and have fun with it