[pinholecam]

A high end APS-c sensor like in the D7000 and K-5> low to mid FF sensor. Maybe equal to the latter. For proof, try bringing up shadows in the 5DII and III and see what happens.

Good cams, regardless.

+1 to this.
I have/had K5 and 5D and a K30.
The tolerance to PP and shadow adjustment on the K5/K30, run circles round the 5D.

To TS, my advice is to not look at it in this way.
I like to think/'see' that a lens on APS-C and/or FF gives me a certain working distance/FOV/DOF.
Thinking too much over the 'what it could have been' of FF lenses used on APS-C; equivalence; etc just makes one despair and bitter like the many FF proponents that linger here.

[dtmateojr]

Is the purpose of FF just for shallow DOF only? Is there any IQ different between a crop with fast lens (33.3mm f/2 ISO 3200) vs FF slow lens (50mm f/2.8 ISO 6400) assuming lens have the same quality, sensor has the same technology, DXO standard ISO?

You won't know which sensor was used to capture a shot without looking at the EXIF data.

The negligible differences will only show up outside of real photography, (i.e. shooting test charts).

[Aux]

Sensor size alone means nothing, image quality depends on the whole optical system and method of processing raws. For example, DAL 18-55mm kit lens is very sharp on k100d, but produces awful results on k30. Is it bad or good? Correct answer: it depends.

The same goes to sensors, size by itself means nothing at all. Bokeh depends on sensor size, its filters, pixel size, focal length, lens quality, aperture setting and a way you post-process image. Size is only one variable.

It's like fuel consumption, big and heavy diesel truck eats a lot more fuel then small petrol powered town car.