Interesting, I didn't know the Speed Graphic didn't have an equivalent to the 35mm world's SLR flash sync speed, like 60, where the first curtain opens, syncs and then second curtain closes...
Lens shutters would solve that problem, certainly.
I sometimes use flash bulbs with 4x5 rangefinder, because I am shooting a Grafmatic with 6 shots. Maybe I am prepared to shoot 24 shots max if I am ambitious, for any one excursion.
A small flashgun with a handful of bulbs is reasonably lightweight and fairly convenient for the purpose. I'm not taking that many pictures, so the fact that I only have a few total flashes is not as significant when shooting 4x5.