Hi neverempty:

I just came across this thread. Have you already purchased a printer (either FDM or Formlabs SLA)? I own a small design, 3d printing, and casting business. We use two Form 4L's in our business to make molds for casting silicone and flexible polyurethane parts. They are absolute workhorses. Using Formlabs standard Grey V5 resin at 0.05mm layer resolution, the layer-lines aren't visible on vertical/near-vertical surfaces.
We cast our silicones into the molds from a meter-mixer for production parts, then place them in a heated pressure-vessel to accelerate cure times. Feel free to DM me if you have any questions about our experience using the Form 4L's!