I actually cannot recall my highest speed number, but I remember where it was. I had gone up to N GA for a vacation and took the bike from Vogel to Blairsville for the day. At that point you are pretty much already down the mountain, but there is still a decent grade. I had ridden directly out of the park and wasn't really loosened up yet. Coming down I got up to speed (I imagine around 40 or so) and developed a speed wobble that made me about crap my shorts. I was lucky enough to stop it with the knee to the top tube.

Don't really care to go downhill like that again, at least not on a DF.