Sigma 70-200 for pentax

[Kit]

Just wondering if it's worth while investing in a sigma 70-200 with optical stabilisation when the K5 already has shake reduction built in. Price difference is nearly $1000, but would rather buy the correct lens straight out. Any thoughts?

[i speak in math]

Just wondering if it's worth while investing in a sigma 70-200 with optical stabilisation when the K5 already has shake reduction built in. Price difference is nearly $1000, but would rather buy the correct lens straight out. Any thoughts?

while I don't have either lens, I've heard the previous model w/o OS is sharper and cheaper. But since its not made, its tougher to find. There are always ones on sale over at the pentax forums, or keep your eye on KEH.com.

[Conman89]

Buy a Cannon and don't look back the cheaper lense can cause serious problems not to mention poor picture quality.

[i speak in math]

Buy a Cannon and don't look back the cheaper lense can cause serious problems not to mention poor picture quality.

LOL -- here's one! Buy a Cannon

What is this cheaper lens you are talking about? What problems would it cause?