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Tuning cachesize

I'm using OpenLDAP 2.4.7 with BerkeleyDB 4.6 on Solaris-10 hosts.  We
haven't been using it in production so I don't have any real experience
with the performance under load.  I'll be looking into doing some
simulated load tests later.  Right now, I'd like to understand more
about performance tuning.

I'm trying to follow the instruction in the FAQ or OpenLDAP Software 2.4
Administrator's Guide section Calculating Cachesize but can't
find information that is needed to calculate the cache needed for
various indexes.  In particular the formula given near the end of that
section talks about the "Number of hash buckets".  I've found something
that could be it from running db_stat -m command's output, but that
seems to be a single number for the whole database not one per index.
Would someone point me in the right direction?

BTW, I get much larger cachesize using the Admin Guide/FAQ method vs.
the method Quanah Gibson-Mount wrote about in this mailing list.  (du -c
-h *.bdb in the database directory)  Is that expected?

I assume it would be best to try to optimize the cachesize for all
databases.  Does this include the log database used for delta-syncrepl?

Also, is it better (performance wise) to give more memory to the db
cache or the entry or idl caches?  I couldn't find a clear answer from
the Admin Guide, FAQ, nor the mailing list.

Finally, is there any difference tuning bdb vs. hdb?  I would think not,
but since I'm asking...