I'm kind of in the same boat. I have the 70-200 f/4. I'm planning to sell this lens and get either The 70-200m f/4 IS version or the 70-300mm f/4-5.6

Right now I'm leaning toward the 70-200mm f/4 IS because it's sharper at 200mm and I don't think I'll get much use at 300mm. Also the difference in weight. The 70-200mm f/4 IS is lighter.
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