[Vinelander]

I cannot personally judge any of the other lenses, but I have owned a Sigma OS for several months now (first Nikon, now Pentax) and it is a very impressive lens. Its only weakness is at 200 mm wide open, where it is a little soft (sharp enough for normal screen/print sizes, but no so much at the pixel level); anything else is sharp (as in "pixel-peep-sharp"), and between f/4 and f/8, very sharp (as in: you could use near 100 % crops as your final photo). Then again, from what I've seen on the web, you will need to look closely to see the advantage over the Tammy.

I would definitely recommend getting a lens with an integrated optical stabilizer. Having the picture stabilized in the viewfinder can be a huge help with accurate framing. Also, at least the Sigma's OS is just a tad more reliable at very slow shutter speeds than the K-5's shake reduction system. When comparing I found that both are quite capable down to about 1/20 s at 200 mm with medium focus distances (and solid shooting technique), but the keeper rate with Sigma's OS is noticably higher.

[Talos]

Thanks for the feedback guys. I'm leaning towards the Tamron atm. Just hunting around for a decent price locally here in Australia.

[pdrury]

What about this discussion in the context of indoor sports (ice skating). For this I need the 2.8 aperture but just as important (or more) is focusing accuracy. Using a K-5.
I considered the Tamron - gets great reviews for sharpness but mixed when it comes to focusing (ie fast for a screw drive but slower than Sigma's HSM).
As the ice skating image challenge is about movement in low light, will the Tamron just not cut it?
The Sigma is probably out of my price range - although my kids are only young once so just I just accept I need to pay this much to get the accuracy I need?

Grateful for any advice!
thanks