Yup, you can go pretty fast on a Dahon speed pro TT and some of its other models. My Dahon, which is on permanent loan to a friend, is a fun little bike for leisurely commuting and cafe rides - not fast. I can go a fair clip on my Brompton though and overtake many full size bikes on my eight mile ride to work. But that's a short ride with traffic light stops. So, as was said earlier, it depends on who you're riding with but also what folding bike you ride. The ones that are built for speed tend to be pretty pricey though.