I was pondering this last night while observing. I would like to stay with F/13 if at all possible but the cantilever of the mount is a problem. Unfortunately, the GEM uses cantilevers at every possible oppurtunity while a yoke mount doesn't use them at all. With a long OTA critical balancing would become much more important but I don't mind spending an extra 10 minutes getting as close to perfect balance as possible. When you say serurrier equivalent what do you mean? I thought the point of a serurrier truss that it flexes equally on both sides. I think a horseshoe would be better than a yoke because of the bigger bearing surface and the ability to observe faint galaxies in octans
. On a different note, the original problem solved itself( the decreasing sagitta) so now I can sleap knowing my mirror is behaving.