Slow replication in mirrormode

I've moved to new (FAST*) hardware and I was testing how long it took for a empty mirrormode server to catch up with the other one. (like after a complete failure of one of the nodes)

I'm using a database where id2entry.bdb is ~6.6Gb. and it's taking surprisingly long time. After 18 hours it has gotten around 1/4 of the way.

I'm wondering if I could speed it up by loading an LDIF backup on the empty server before I start it. Are there anything special I should take into account, like regarding entryCSN and options to slapdadd when I load the backup?

/Peter