Originally posted by Driline Sigma over the Tamron 70-200? Sigma HSM or HSM II? I'm intrigued by this lens. I could easily swap my DA*50-135 for it. Save myself a grand.
Well if it for AF performance, that for sure sigma, tamron only has the basic screw drive lense that is great and has fantastic quality for the price... But it is not made for sport. Could do the work of portraiture, architectural detail, general purpose tele. But this is not AF deamon. It's AF perform quite ok on Pentax and quite poorly on other maker (the screw drive version) because screw drive AF is better on recent Pentax bodies than on Canikon.
To know if Pentax version would work better than the sigma and if it will be really necessary for you is really a question only yourself can respond.
My understanding is that the sigma is quite good but not as good as the Canikon variant. I'am not sure the Pentax would match the Canikon variant neither but we speak of an unreleased and untested lense here.
I would say it should be worth to spend some time reviewing the lense looking from feedback of users etc and to really justify you need to spend 1000$ more for the Pentax if you choose this path.