For you K-5 owners, how about a simple test?
Looking at the picture in
Noise and DR comparision: Canon 5D vs 5D2 vs 7D vs Pentax K5 where a shot of a wide DR scene was taken with a K-5 at ISO100 and then 4 stops EV boost applied in PP, compared to the equivalent exposure of shooting at ISO1600, you can see how the highlights are not blown in the desk lamp when using the superior DR of base ISO. (DR decreases with increasing ISO, as already discussed.)
Consider a tricky exposure situation like blowing out candles in a dark room, where you're trying to get decent illumination on a person's face and the cake and not have the candles completely overexposed. It would be interesting to compare the K-5's matrix metering performance (if using Auto-ISO, set the max. ISO to ISO1600, since above that digital "amplification"is used), against shooting in raw using the same shutter speed & aperture at ISO80 in Manual exposure mode and boosting in PP to see if you can get a better capture. (If you've got any candles in the house, this test is easy to stage.)
The other consideration in a candle-lit scene is the WB. It will normally be very reddish from the colour temperature of the candles. Do you leave in that way or, if you're shooting raw, do you adjust the WB afterwards to fix up the skin colour, or do you set it part-way between these two settings?
Dan.