I don't think it makes much of a difference at all.

For the `label: bitmap` fields, the label is encoded as a (numeric) string, so no difference between it being an int or a long.
For the `"label": label` (index) fields in the `SearchAcceleratedBitmapDocumentFormat`, there might be a slight size difference, but I don't think it is substantial enough to matter. I am happy to see it measured though.