Since you've already loaded your database, you can of course easily gather the statistics on how big your DB is, and thus what the required DB_CONFIG settings would be to load it via slapadd in the future.
Cd <data dir>
du -c -h *.bdb
Whatever that total is, is the total size you need DB_CONFIG to be to get optimal performance. In another note, there is no reason to split the BDB cache into multiple memory regions (3 0 2) on 64-bit systems, and in fact past tests I did showed that this decreases performance. I'd suggest (X 0
- instead (where X is your updated value based on the results of the
du -c -h *.bdb command.
Also have a read of these two pages for more info: