I've been shooting my daughter's basketball games with a k-x and a tamron 70-200 f2.8 the past month or so. I'm a beginner and although I did get some pretty nice pics, I feel the tamron AF is a little slow. I've seen this same lens coupled with the k-5 on a youtube video and it seemed to focus waaay faster on the k-5. Some say the Sigma 70-200 f2.8 is a much faster lens especially the old non-hsm, non-macro version. Do I buy the Sigma lens or do I spend almost twice as much and get the K-5???...and do not say buy both. haha, not an option right now.