In case it is helpful at all, I’ll post what I ended up doing. The bookshelves are floorstanding but quite tall, standing about 4 inches below the ceiling. I just set them up then, screwed a piece of 1x2 to the side of each bookshelf close to the wall, snugged up tight to the ceiling. Then I tightened the adjustable feet to make sure it was tight. With books filling the bookshelves, you can’t see the 1x2s.
So the bookshelves are essentially wedged into place against the ceiling. They cannot fall over, unless the sides collapse catastrophically (they are open, ladder-like assemblies predrilled for shelf supports. IKEA Ivar, if you are interested.)
But like most things IKEA, these are made with the minimum structure required, and while they don’t lean or rack, they do bow from side to side a little. So to control that, and to add an additional level of protection, I stuck a 2x4 to the wall using six large 3M Command adhesive strips, and then bolted the shelf uprights to the 2x4. Rock solid, and no vibration.
Command strips are removable, even after years of use. Each large strip can handle about 5 pounds in shear, so I figure they can handle more tension perpendicular to the surface. Anyway, the forces as it begins to fall would be very small. Again, the shelves came with a little piece of nylon strap that you are supposed to screw into the wall with a single cheapo anchor, and that is supposed to be sufficient.
So, no anchors!