Well... I stopped by Rapid Transit Cycles last night and test rode a couple Dahons, the Curve D3 and the Speed P8.
So much for my insistence on a 16". The Curve just didn't feel right for me. I had the seat at minimum insertion (which makes me nervous) and it still felt too short. I was getting quite a bit of handlebar flex. Also, the gearing isn't right for my riding style. Too much gap between 2nd and 3rd, and 1st gear is largely useless for someone who rarely encounters hills. I wouldn't want to ride a Curve more than 3 or 4 miles. Good brakes though.
The Speed, on the other hand, was very encouraging. The seat felt right about a couple inches below minimum insertion, the ride seemed less flexy in general, and after a couple minutes I forgot it was a folding bike. The gripshifter was a POS but the drivetrain felt pretty good. And like the Curve, good brakes.
I guess I will set my sights back on the 20" Downtubes.