The Pentax has +2/3 stop improvement in color depth over the Canon but around -1/3 stop less than the Nikon. Bigger differences can be seen in dynamic range where the K-3 has almost +2 stops advantage at base ISO over the Canon, and just less than -1/3 stop compared with the Nikon. In low light, the capabilities of the Pentax and Nikon are equal but you would be hard put to tell the +1/3 stop gain over the Canon in real world use.
Compared with the A58 the K-3 has a +1/3 stop benefit in color depth and just under a +1 stop wider dynamic range but there’s nothing in it between it and the A77. Where the Pentax leads against the A77 is in its low-light performance.
However, while the K-3 has around +2/3 stop advantage over that and the A58, much of the difference in low-light capabilities can be attributed to the SLT mirror. Nevertheless, the K-3 maintains the lead in our sensor performance rankings, while offering some unique and promising features.