Just in case your are interested in seeing comparable sample shots of the new 24-70mm Pentax and the Tamron 28-75mm, you may follow this link:
Nur mal so: Tamron 28-75mm 2.8 vs. Pentax 24-70mm 2.8 ? Pentaxians
I've uploaded two different scenes, shooting both lenses at exactly the same settings (24/28 – 50 –70 => 2.8 – 3.5 – 4.5)
As long as you are focusing on portraits (on APS-C) the Tamron 28-75mm is an excellent choice. Things differ when it comes to landscape (maybe due to the more modern coating etc.).
But see yourself (would love to show lager files but theres a restriction to 1200x1200 pixel).