Looking at these photos I'd definitely keep it. Don't know if it's the same model as the one I had (75-300 MkIII, no IS or USM), mine was probably the worst lens I've ever used and I don't have a single keeper taken with it. The flower petals look well spaced and clear, and the colours of both pics are clean and clear. Mine had awful fringing and gave a halo effect around the main subject in focus and half the time the pic looked like it had been taken through a thin layer of vaseline. Seriously bad!