If the primary concern is as posted "... hauling around the great outdoors ...", then K-5 is the obvious choice here as it is smaller and lighter. I find the choice between K-5 and D3 rather puzzling as they are really geared toward different segment with D3 being a pro camera and K-5 more of an enthusiast model. The advantages D3 has over K-5 are: 1) build quality, 2) low light/high ISO capability, 3) frame rate, 4) full frame sensor.
K-5's advantages are: 1) lower price, 2) smaller and lighter, 3) can do videos, 4) newer sensor with possibly better DR.
Both are weather sealed and can use legacy lenses.
