DTFB shouldn’t be a problem at 40w. Our makerspace has an 80w Rabbit, but the best settings for cutting DTFB are well below 40w. As others have mentioned, cutting it an a single pass creates a concave pocket on either side of the cut (melting foam), but for FliteTest-build techniques, this is actually a plus!
Others striving for a straight (no-pocketing) cut have gone to a 3-pass cutting strategy, 1st pass cuts the top layer of paper, the 2nd (very low power) pass cuts the foam, and the 3rd cuts the bottom layer of paper. With the photo-registration capabilities of the GF, I bet this could be done as well.
Btw, I too am looking forward to creating foam, balsa, and ply pieces for RC aircraft!