In addition to the longer-term pipe dream of building my own 19th century house from scratch, though, I had the epiphany that these 4'x8' classic double-hung windows that have such a poor R value could easily be fixed the same way Hungarians do it in older buildings (and this is surely the same in older buildings elsewhere in Europe) - simply provide a second layer of casement windows on the interior of the window. In fact, with a bar 5 or 6 feet from the bottom of the window, you could have a tilting horizontal casement window at the top that could let in a nice breeze without scattering your papers on the floor and being proof against minor rain, while still leaving the larger bottom part for opening in full when you want to lean out.
I've tried to find a picture of these interior casement windows, with no luck. I don't even have any that I took myself. Just picture it in your mind, and trust me: it would be the perfect modification for the windows in this house.