Barely bigger at all if that holds up.
Quote: I'd rather have a Nikon D750 sized camera that can be backpacked all over kingdom com without breaking my back...
Nikon D750
840 gm, 149x113x78mm
Temperature: 0 to 40°C/32 to 104°F; humidity: 85% or less (no condensation)
K-3
1240 gms, 132 x100 x 77mm
Operating temperature: 14-104°F (-10 to 40°C)
Weather resistant: Yes (92 special sealing parts)
I'm not seeing the D750 as in the same leagues as a K-3 in terms of out doors, and having had two cameras covered with condensation on the last few nights, I'm not so sure about leaving a D750 out where there might be condensation for star trails. So an extra 400 grams for weather sealing, a much lower operating temperatures.
There are a few things missing from the D750 I wouldn't trade weight for. Since I regularly use my camera in -20 and moist conditions.
I can't ever remember a K-3 breaking my back, , in fact I can't remembers a K-3, DA 18-135 and DA*60-250 ever breaking my back... but, I guess all backs are different.
Image with dew covered lens and camera... I kind of like it.
With Pentax, no worries....