For instance, this is K-3 Vs D7100 Vs K-500 Vs A7 at ISO 1600 in RAW for the centre of the test shot image:
http://www.dpreview.com/reviews/image-comparison?attr18=daylight&attr13_0=pentax_k3&attr13_1=nikon_d7100&attr13_2=pentax_k500&attr13_3=sony_a7&attr15_0=raw&attr15_1=raw&attr15_2=raw&attr15_3=raw&attr16_0=1600&attr16_1=1600&attr16_2=1600&attr16_3=1600&normalization=full&widget=1&x=0&y=0
So, measurebate endlessly yourself to go figure all the differences for all other combinations of different camera models and at different ISO and etc. I blog, you decide!