I just went through this decision process (for a K20D as well) as I seem to be doing a lot more portraits, though I finally limited my choices to the Tamron 28-75 and the DA 70.
In many ways I wanted to go with the Tamron; relatively fast at 2.8, the range would handle full body to head shots, and I had used it before on a borrowed Canon. I knew it was a good lens.
But in the end I couldn't resist the allure of the 70 Ltd. The magic of the Ltd series, the small pancake design ... that damn DA Ltd lens club thread ...
I don't even know how to really use it yet, and the images are blowing me away. No regrets here.