Yes, it is basically the same engine with a different map and slightly smaller injectors.
It can be remapped to give more power than a standard 320, but not quite as much low down torque.
Like this: http://www.superchips.co.uk/curves/merc280cdi.pdf
My experience with a E280 CDI is that you end up with a sweeter and more powerful, if not quite so 'grunty' engine as the 320.