I've heard that the Tamron is good, but I do need the AF speed.
Can't use the AF-D except as a MF, as my D5100 does not have a built in motor. My D70 does, and I already have a 80-200 AF-D to use when I need to on it, but want somethign for the D5100, which means AF-S. It's either spend $1K now on a 80-200 AF-S,and later sell it and get the 70-200 VR, or wait a while to spend $1500 for a used VR.
Or, I could get the Sigma IF it is going to be good enough that I wouldn't ever need to upgrade. I've heard good things about Sigma's HSM speed, and that their AF on the lens is good, and that their OS works also. But I've also heard that the lens is soft except for the extreme center when at 200mm. Think towards an FX future, I like to buy lenses that will work with future bodies, which buying the Nikon protects.






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