been around 170 on my modded 636. it seemed really stable for such a high rate of speed, cars doing 70 seem like they're sitting still.
i think the human brain starts to fail at comprehending speed at about 130 or so. and speaking of 130 i took a spin the other day and met the county boy at about that speed. scared the shit outta me b/c i don't ride a whole lot anymore, i just put my head back down and gassed on it. came back in my car after i got home and sure enough he was still patrolling, looking for me.