I noticed that the sawmill cuts logs into planks, then slabs, then sticks. However, I would like it if you added a stair conversion just before the slabs. This way, it becomes more efficient than vanilla crafting, and fits with the sawmill's purpose.

I'm not quite sure how to handle the resource math though. Maybe 1 plank > 1 stair > 1 slab? That would make slab crafting less efficient overall, but more useful when you only need 1 or 2 slabs. If 1 stair > 2 slabs, it would retain efficiency, but less realism, but this is Minecraft, so it could work.

I'm on board with this. Out of balance considerations, 1 > 1 > 1 seems more attractive, since log cutting already produces more planks than manual crafting. On the other hand, the time required may make the recipe even less useful.