[falconeye]

Is it possible that the K5 tends to expose to the right more than the D7000 and then ACR knows to bring down the exposure in post, producing less noise and the impression that the K5 requires a longer shutter speed for a similar exposure at the same iso? I know the K7 tended to do this to reduce noise.

I have no conclusive explaination I can offer.

I am wondering if this hasn't been already discussed and clarified by somebody else in the past.

As for exposure to the right. That's a concept applicable in matrix metering. However, in spot or center weighted, the ISO 12232 norm applies and the vendor has to pick a calibration constant (which isn't standardized) and Pentax is known for their relatively consistent choice of constant.

DxO recalibrates all measurements by using a saturation-based ISO measurement, the best method applicable to raw files. I fear that all JPG-based tests yield somewhat arbitrary results because of inconsistent metering. While it could be very simple indeed: Just shoot with standard values of shutter/aperture for a calibrated light source and using primes with almost no loss of transmission.