Berkeley DB Family

I'm considering using BDB to store fairly large numbers of keys (mostly RECNO, so 4 bytes) with very simple data (probably 4-8 bytes at the most.) I expect to have around 200k nodes, and was wondering how much space overhead the btree structure would give the file. With 200k nodes, and ~12 bytes per record (key + value,) the basic content of the database would be around 2.3 MB. Would insertion order affect the overhead (i.e. fragmentation, if such a concept is relevant) if I allowed duplicates? I would be adding the records in recno sequential order, so I don't need to worry about allocation of intermediate keys.

Thanks,

Daniel Peebles