I usually go with a 1/2" s/a as well. I decided to double it over, especially on the silk. The silk doesn't give at ALL, and it frays like crazy, so I figured extra protection would help. As it happens, folding it over twice isn't really any more work than once. I decided to do the linen in the same way, as well.

I *think* I have my plan in place - thank so much for the insight. I'll be posting an update today, with more seam diagrams!