I use silk thread most of the time for appliqué- which I do a lot of. Right now I think Superior Threads is having a sale on their silk threads. Most of my silks are YLI and Sulky. I do have a few from Superior Threads too.
100 wt silk is very strong and very fine thread. I also have some 60 wt silks. Silk pretty much disappears on appliqué and is wonderful smooth thread to work with.