Xmeda,
Thank you for the detailed and quick reply!
Shooting close sports (basketball, volleyball, etc) with my Tamron is the main reason I am looking at the Sigma - particularly this one:
Sigma 70-200 f/2.8 II APO DG HSM in padded case. REDUCED + FREE SHIPPING - PentaxForums.com
The owner says he has had no difficulty shooting on his K-P or K-1. If the autofocus is faster, that is my main interest over the Tamron.
For birding and wildlife, I have the 150-450, with which I am quite happy.
Thank you again!
--Jonathan