Simon,
How low do you call low, in terms of Revs .....
Even my old Turbo 4.2 Diesel didn't particularly like taking off from 800 Revs in Top Gear after dribbling through town ( although it would do it )
The Auto would never ever let the engine get so low, so you don't notice in the Auto....
My CRD is good from around 1800 rpm usually. I roughly drive in the 1500 - 3300 rev band ... no need to go more or less to get where you need if you are in the right gear