The -400 has triple slotted kruger flap set up, giving a larger increase (% wise) in surface area by comparison. (Result of more sweep I suppose)
Airbus is all hydraulic, -400 LE are preumatic.
-400 partial LE retraction on reverve thrust application (inbd and midspan) due design (can't remember the name, but they just fold out instead of slide out.
Lots of smaller differences from a handling point of view, but that's all I can think of fo now.