I also have both. I do like the DX's large screen but when I am reading in bed, it's just too heavy. My wrists start to ache from holding it. And it's far from what I'd call 'portable'.
You need to decide which is more important to you. If you want something you can carry in a purse/briefcase, go with the K2. It's light and easy to carry around.
If you want something to read technical documents with a lot of pictures, or magazines, or newspapers...go with the DX. That larger screen is wonderful.
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