High output moving iron: The lower the load resistance, the more it will roll off. There is a particular resistance value such that the cartridge will neither ring (overshoot) or be rolled off, this value is known as the 'critical damping' value.
If at critical damping, the cartridge will not have reduced output in any way.
Please note that when insufficiently loaded (load value too high) the cartridge will 'ring' (distort). The distortion will interact with the human ear/ brain system in such a way as to suggest that it is more dynamic. Don't be fooled by this physiological phenomena.
None of this applies to low output moving coil cartridges- that is a different discussion entirely.
