I was surprised when you said the greybark risers were made out of birch, because they seem heavier than birch to me. Maybe they are stabilized. Probably worth asking BW. The ironwood risers are beautiful, and probably heavier than the PSA. The only thing I didn't like about the ironwood was that the finish was silky smooth, and I preferred the slightly knobby finish of the greybark as it seemed to have a somewhat more positive grip. This was years ago, and the finish may be different now.