I think you should do your homework before you buy your toys. Tamron 17-50mm F/2.8 VC is soft from most of reviews. However, the non VC version is very good. Before I upgraded to FF, I was checking may reviews and even test Canon 17-55mm, Tamron 17-50mm VC, and Tamron 17-50 non-VC. Canon 17-55mm was the best one and I had good time with the lens for about two years. After I upgraded to FF, I used Canon 24-70 MK1. Honestly, Canon 24-70 MK1 is not sharper than Canon 17-55 at all the time. I believe that's because the IS feature on Canon 17-55mm. I was so excited when Tamron released the 24-70mm VC. After three months waiting for reviews, I decided to give the Tamron 24-70mm a try. Guess what? I sold my Canon 24-70mm in two weeks after I use the Tamron 24-70mm. It's sharper than the Canon 24-70 MK1. Moreover, I am happy with the VC feature. I have some shutter speed about 1 second and they are still good. That's almost impossible to happen on my old Canon 24-70mm.
Buying from third party companies like Tamron, theres all the time risk that something will be wrong. I have canon 550D and Tamron 17-50mm f2.8 VC for about three years. I'm not happy with 17-50mm f2.8 VC, difficult to get it sharp, its soft at f2.8, sometimes I get errors, time to time a lot of mist focus shots and sometimes I even not sure if it suppose to work like this. You must to get used to them and when you'll be able to make good shots.