Weight: system more important than sensor size?

I do not know if you paid attention to the other posts; what you are looking at is the OM-D5 with 50mm lens and D800 with 85mm lens on it.

http://forums.dpreview.com/forums/post/50307669

So it is not even equivalent from the start. Yet when downsizing double ISO (ISO6400) D800 frame to the 100% of OM-D5 it still neither loses detail not adds additional noise to it. In fact I can balance it to look exactly the same. It would have been entirely different had we compared 50mm on OM-D5 and 100mm on D800 instead.

Why resolution is good, for several reasons. First, if you shoot at high ISO and you want to clean it up, it let's you do it quite nicely. The second point is the opposite, if you want to sharpen the image, it again allows you to do it without those familiar artifacts that are so common with the smaller cropped formats. There is plenty of room in every direction.

Now whether the weight is important or justifiable to you is entirely different story. You can have lots of lenses in your bag and you can always carry them somewhere, somewhere, I can do with less. In fact I have several backpacks that work quite well, but even at that, most of the time I get by with smaller formats just as well.

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-sergey