I don't know if this will be in the Pentax mount. Before I started switching to Canon I called my contact at Sigma corp. office in Japan and asked if there were any updates to the supertele lenes for Pentax in the near future. He may be just jerking me around. But after a week of checking he said no plans for Super tele's for Pentax planed in the near future. Hummmm
I hope he is just playing it safe with the info and not saying. It would be a huge deal for the 500mm f4.5 to be reworked. OS, HSM, splash froof, and better optics for Pentax would really put Pentax back in the hunt in my opinion. I have pretty much turned the corner now. Hope Pentax gets this it would be something to see.
I asked after the 100-300 was anounce because I thought it might be a turning point. But he killed it for me.
Here is a test against the Canon 500mm f4L and the 300mm-800mm F5.6 Sigma.
http://www.pbase.com/liquidstone/image/58879465/original
The Sigma is very impressive. I have shot with a guy that has one in Thailand and it is a monster. Just way overkill for the jungle, 5.6 to slow and too heavy and awkward for me. But he said on the ocean and out in the open it rocks. Not my cup of tea. But for some of the guys it would be great.