I just noticed the new test result on ephotozine website. It looks promising to be a bit better than the Sigma equivalent. According to the charts, 70mm - 135mm seems even better than Canon MkII. However, it falls a little short at 200mm, which is more important to me. I guess we can't make conclusion before seeing more reviews and real photo samples.
http://www.ephotozine.com/article/tamron-sp-70-200mm-f-2-8-di-vc-usd-lens-test-20748
http://www.ephotozine.com/article/tamron-sp-70-200mm-f-2-8-di-vc-usd-lens-test-20748