Both Nikon D300 and Nikon D2Xs have APS-C sized 12.0 MP resolution sensors so sensor size and resolution is not a differentiator between these two cameras.
Below you can see the D300 and D2Xs sensor size comparison.
Sensor Size and Resolution Comparison image of Nikon D300 and Nikon D2Xs Cameras
Nikon D300 and Nikon D2Xs have almost the same sensor size, so neither of them has any significant advantage over the other in terms of providing control over depth of field when used with the same focal length and aperture.
DxOMark Sensor Scores
Both Nikon D300 and Nikon D2Xs sensors have been tested by DxoMark. DxoMark scores camera sensors for color depth (DXO Portrait), dynamic range (DXO Landscape) and low-light sensitivity (DXO Sports), and also gives them an overall score. Of the two cameras that we are comparing, D300 has scored 67, 8 points higher than D2Xs.
Model
Overall
Color Depth
Dynamic Range
Low-light ISO
Nikon D300
67
22.1 bits
12.0 Evs
679 ISO
Nikon D2Xs
59
22.2 bits
10.9 Evs
489 ISO
Sensor size sets the circle of confusion, so it drives how much depth of field each
of these bodies gives you at a given aperture. You can calculate it exactly for the
Nikon D300
or the
Nikon D2Xs ,
including hyperfocal distance.
