Thanks mikekeswick and Springbuck. I kinda thought plainsawn had similar attributes to peeling a stave down to one growth ring (grain-wise anyway) - just wanted someone with more experience than me to confirm it.
Yeah, that's right, and that is why a plainsawn board with nice parallel rings visible toward the edges is a great choice for a board bow. The TL:DR of my post is that not all QS stuff is the same. I would use a really nice flat sawn backing, too. I just saw a bow here where one of us PA guys just took the wood under the bark just like a stave bow, and made an elm backing.
Let's say you took a nice, straight, round hickory log and split it exactly across the rings, so that every ring in both halves was now a semicircle. The best possible hickory backing would be obtained by smoothing the flat, split sides, and taking your backings from right there on that surface. Got it?