I can't compare focus speed to the Sony - the Tamron is not fast at 200, that's sure, but somewhere there was a video showing that the Tamron is still faster than the Sony. The issue is, that due to the shake, at 200mm the camera has a problem to find some contrast. My trick is to half-press the shutter to activate VC and then it locks much quicker. And then, I have the NEX-5, 5N/7 should be faster with AF. In any case, an 18-200 is always a compromise, it was the same with my Sony A-mont 18-250.
Btw, I am now nearly A-mont free, sold the A700 and CZ16-80, just a beercan remains. I was sure to get a NEX-7, but since the A57 I think there might be a downscaled NEX-7 later this year, with the 16mp sensor.