As far as I know, the fundamental geometries of the Silk models and those of bikes in Bike Friday's Pocket range (which includes some less expensive models) are the same. If I pay attention, it feels like the long seat post has a modest vibration damping benefit relative to a regular road bike... mostly I don't notice or think about it!
Bike Friday is good at striving towards what I think folding bikes should be:
A bike that fits the rider that happens to fold (or pack).
I've got two bikes, one folds, one doesn't. The fit is almost identical between the two. It also happens that my longest ride is on my folder.