About glassware: I used the Tamron 28-70/2.8 for years, but somehow lost it. Last year I was treating myself to the Nikkon 28-70mm F2.8, and expected it to outperform the Tamron by far. In reality it is quite the opposite: The Nikon is extremly chunky, does not handle very well (esp. if using manual focus), and does not deliver anymore brilliance than the Tamron. Through the viewfinder it even appears a bit darker. Another fact: Both of them look poor compared to a good fixed focal length lens. You won't see it in the sharpness of your pictures, but lens flare and esp. contrast when shooting against the light is where the fixed lenses are just the best (for sure now this is the large format photographer talking).
Camera-wise I am very happy with my Sony RX1R, but I guess not being able to change the lens is not an option for you. But this 35mm Zeiss is just brilliant!