Any ORM adds some overhead to all the database operations; and to measure it well (i.e. to measure mainly the overhead), you must minimize the database load. That's what we do.
If we measure the efficiency of intermediate layer, we must make all the layers behind it operating as fast as possible - to measure just the efficiency of that intermediate layer.
And although it's clear that on real life tests difference must be much less significant, it still will be there.
