I might have to get the Tamron I think since it is such a gamble with the 16-50. I prefer Pentax. I have the Tamron 28-75 as I needed a zoom lens for my holidays and didn't want to carry my primes with me. That one is a bit of a hit and miss for me. I know that lots of members here rave about the Tamron 28-75 but I find that it is not as sharp as my 77ltd. So I am not too keen to get another Tamron if I can help it hence the 16-50. Can't say how disappointed I am that so many people have problems with it!
My plan was to get this 16-50 and sell my Tamron 28-75.