Need Lens advise -- 24-70 II 2.8 vs 24-70 IS F 4.0

Need advise, I bought the D6 with 24-105 -but the lens is not as sharp as I like.

I mainly shoot landscapes - I am leaning towards the 24-70 2.8 vs 2, but the

prices is a concern. So love to see some shots and your advise.

Thanks!

Joan

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Nikon D700, Canon D6, Leica X1, and Sony rx1
www.pbase.com/joanteno