This comparison is based upon the Imaging-Resource Still Life standard JPEG ISO test.
The selection of the D300 40D and K100D cameras for this comparison is primary based upon a DPReview user called Anastigmat's
repeated hilarious postulations, that K100D has more resolution than the D300 camera at ISO800. Check for yourself and make your own conclusions....

Lenses used:
D300: Sigma AF 70mm f2.8 EX DG Macro at f8
40D: Canon EF 100mm f2.8 Macro at f8
K100D: Pentax DA 18-55mm f3.5-5.6 AL at f8/55mm