You can just make a 10 strand unpadded D97 and you will be fine with or without overlays. Really soft wood like elm or hackberry I wouldn't trust so much without overlays. If you don't feel like padding 6 & 8 strand strings that is. The speed loss is minimal if measurable. The only draw back is you use a fuzz more materials.
As for tillering? Make yourself a 62", 64" and 66" 12 strand string to leave on a peg in your shop. One will fit 95% of what most people build. For example. You can use the 64" for a low brace tillering string. Then grab the 62" to get to final brace. Works great.