I'm not sure the exposure is better on the K20D? Shooting Raw would make it very easy to get what you wanted on either one of these...however, if I am not mistaken, f 5.6 and F7.1 do not deliver the same amount of light anyhow?
What I have noticed...personally....it is harder for me to get what I want from my K5 when shooting people than it was with my K20D. Since I have been able to get some from my K5 that met my expectations, I feel sure this is due to some differences in the two cameras that I have not adjusted to....after all, I took thousands of shots with the K20D and learned its behavior...have not done that yet with the K5. It was the same when I went from the K10D to the K20D....I conclude that this is normal procedure with a new camera? Or, it could just be the damn Squirrels have ruined my ability to shoot people......?
Best Regards...take some more and post them, we will tell you what we think and someone with more knowledge than me will help you adapt to the K5, it is a fantastic camera...in case I haven't mentioned that.
I got my K5 a few weeks ago and for the first ten days or so, I was constantly comparing it to my K20D. I was sure that it was inferior to my K20D, so many "problems". But the thing was, for me at least: I loved my K20D, I'd gotten to know it really intimately, and the K5 was new and I wasn't used to it yet, so I was sure I'd made a mistake in buying it ... until I climbed up the learning curve somewhat and got somewhat comfortable with the K5 and now OH MY GOD! I love the K5, for me I now prefer *almost* everything about it to my old K20D (I do still miss the K20D's plastic-door terminal cover, bit I suspect I'll get over this). It *did* take me awhile to adapt, though.
+1 on the pinks that Raybo mentioned...the haze will go away with the proper colour setting...
Also, Try taking shots from 2 different films that are the same ISO using the same settings on the same camera....they can have different properties. Same for digital...different sensors and different electronics. My K-5 is much better with dynamic range and high ISO, but I preferred my K20 and K7 for more natural tonal rages. It's all good, but overall the K5 is much better.
The WB is a problem (or a difference at least), but clearly not the only one. Because the main thing that makes the K5 one look worse is lack of contrast, and you can see it's more prevalent in the middle and upper parts than the lower parts. Which is what makes me thing it's flare. And the fact that it's different lenses makes that all the more likely.
If you take a look at DXO for the 16-50 lens test you will see that it's true maximum f-stop is actually higher than f2.8 (smaller diameter). If you are using different lenses then you could have one a third of a step/stop higher and the other a third of a step/stop lower (than indicated) giving you the two-thirds stop difference those photo's indicate. Also, metering is 'analog' while aperture selection is essentially 'digital' and limited to the positions indicated by the numbers on the aperture ring, or their equivalent on lenses without the ring. I have an old 55 f1.9 lens with the aperture ring out near the filter threads which has a very long 'throw' for aperture selection. I'm able to essentially select an infinite number of aperture's with this lens as the blades move as you rotate the ring, even between the numbers (4, 5.6, 8, etc). The camera meter will still only select a predetermined speed (1/125, 1/60, etc). This leaves You with a limited number of combinations for exposure. Modern camera's may induce EV into a photo for more precise exposure, I'm not sure. They certainly are capable. One of the experts here on the forum may have that information.