I have had very good experiences with the Sigma repair operation in Duluth, GA.-called Camera Repair Japan. Every lens that I've sent there(non-Sigma, also), has come back quickly, AND focusing more sharply than when sent. I haven't spent more than $200 yet on a repair, with CRJ. and some I wondered about even getting an estimate. I hope your experience is as good as mine-wish I could say the same for Tamron-I've been completely underwhelmed by their service, It may be lightning fast, but both lenses I've sent have come back softer than before they were sent.

The biggest difference, from my experience, that you will notice, will be color rendition and contrast. The extra clarity is nice, but the color is superb. I saw these differences using my T3i and 70D bodies. If your body is capable, definitely take the time to "dial-in" the lens/body combo with the AF Micro adjustment.