http://www.pentaxforums.com/userrevi...uct=320&cat=74

http://www.pentaxforums.com/userrevi...uct=321&cat=74

http://www.pentaxforums.com/userrevi...uct=518&cat=74

Not sure exactly which lens you are choosing. Here are a couple reviews of the 70-300 Sigma lenses for Pentax. These Sigma lenses are all the same, except they are built with different mounts. It is the only difference so the reviews will be consistent with those built for Nikon, Canon, etc.

I bought a Tamron 70-300. It also had a macro function on it. It was the way to use the lens. It was complete garbage and I would not recommend it to anyone. It does not reflect on the Sigma as I have no tried that one.

If it were me, I would spend as much money as I could on a lens, preferably the prime. I like primes. Macro is nice, but its better to have a nice prime over a sub-par macro. Not only that, it isnt even a true macro lens. You will get 1/1.5 at best, and it will not be sharp. Macro is typically 1/1 and will be pin sharp.