I haven't hit anywhere near that fast on my Dahon Speed; Top gear is only 85 gear inches, can't pedal down fast hill. Feels inherently less stable, I hold the bars firm. No wobble if I stay seated or seat clamped between thighs if standing to create drag, off seat and it can wobble. I'll brake before fast turns, that's what wears my brakes and rim sidewalls, why I want discs, plus for rain.

On my 700C racer, crit geometry but felt rock solid at speed, on a mild downhill, long, straight, I topped out the computer at 64 or 65 kph. Original Scott clip-on time trial bars. That Cannondale frame was very torsionally rigid, I think that's why I never felt anything approaching speed wobble, I was ignorant of that then.