You are a professional doing this? If there is no + as I understand the financial issue is important to You, then without hesitation take the Sigma.
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If it brings some income or You are photographing in the Studio, and native Kanarovska blaze, of course would be preferable. And faster and synchronize better build quality again.
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I was choosing between the 430 II, 580 II. Took the 430, as the needs in page not as big. The Studio don't like the extra 30% of the weight I don't need, reload speed, 430 arranged.
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So I think You first need to decide for what purpose you need blaze.