To revive this thread briefly from the dead, here's the sequel.

I modded up my Downtube 8H with the butterfly bars and MKS EZ AR-2 QR pedals with half-toe clips. I also put a Marathon Racer in front and a Big Apple on the rear.

Riding my 8H felt appreciably faster after this event but... well... I finally sold it this week. I decided to try a full-size road/touring bike (Jamis Aurora) and found it better designed for my purposes (doing a very long ride at a reasonable speed). Yes, I know I could be fitter and spin faster and wring my performance and speed out of my folding bike, but why not use a bike that is really designed for the task at hand? Going fast on my road bike just feels so much easier and more comfortable without killing myself, and that is what I needed and wanted.

Meanwhile, from the folding perspective, I found I was just happier riding my Mini rather than my 8H. The mini is much more practical to fold and store and schlep (8H is bulky), and it has a nimble and plush ride. It's also extremely cute. I get an amazing amount of power and use out of such a small device.

I did replace the stock tires with Big Apples, the 25T rear sprocket with a 23T rear sprocket, and the spring suspension with a Birdy elastomer a la Jur. But I don't need to do any further modding in that direction since I now have my long-distance speed machine and all-around compactness and utility is more what I need for my Mini. Fenders have been a big help. As for further mods, I am considering replacing the one-arm kickstand with a triangular one for more stability, and I thinking of acquiring a QR seatpost rack so I can use it with my Ortlieb Shuttle suitcase.