D600 vs D300s exposure difference.

Just got the D600 a week ago and I'm trying to set it up as close as possible to my D300s. I thought I go out and take a few shots outside with both cameras using the same lens, Nikon 17-55mm, and see how different the metering system react to the same lighting condition. Using Matrix metering in manual mode I got the same exposure reading. But for some reason the D600 exposure is brighter than my D300s. Curious on why that would be, difference in sensor sensitivity maybe? I used the same settings, including picutre controls, on both cameras.

D600 image

http://www.markthompsonphotos.com/photos/i-SpgmrWF/0/O/i-SpgmrWF.jpg

D300 image

http://www.markthompsonphotos.com/photos/i-4GLTVs2/0/O/i-4GLTVs2.jpg

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http://mtt.smugmug.com/photos/245519815-O.gif This is me Post Processing. If only I can get it right the first time! Full time auto tech, part time photographer. Mark Thompson/MTT Louisville, KY. USA Why do you have to 'put your two cents in'.. but it's only a 'penny for your thoughts'? Where's that extra penny going to?http://markthompsonphotos.com