Just a quick question for the group mega-mind. My Tamron 18-270 (older version) bit the dust (literally, I work in the North Dakota oil patch and until they paved some key roads this summer it was like a dust storm every day). I use my 7D for newspaper work so IQ isn't the #1 priority compared to getting the photo right now, and I appreciate not having to swap lenses. So right now B&H has the Sigma 18-250 with a $200 instant rebate at $349 and the Tamron has a $70 mail in rebate at $379. I am leaning towards the Sigma because I don't think I will miss those 20 extra mm and I really don't like mail in rebates. Any thoughts one way or another on these two lenses, especially in terms of durability and weather resistance?