Not an expert here, so just speculating. I don't think the only question is the frequency of the vibration--you don't actually feel that directly. The vibration of the fork is felt by you primarily through your hands, correct? So the real question is how efficiently does the fork communicate this vibration to the handlebars--to the extent that frequency is a factor in this, I would think it would be more of a question of the relationship of the vibration frequency of the fork, the stem and the handlebars. Really, though, I would think that amplitude of the vibration is likely a bigger factor than frequency.

Does this sound right to anyone who actually knows anything about engineering?