Hi fellow Pentaxians

I've decided to bite the bullet and look for an auto focus lens for birding
.
In my declining years my hands are just not steady enough to manual focus and get good results.

I have thought about a KatzEye or similar to see if that helps, but I think that the reality is that I need auto focus.

I have narrowed down my choice to 3 lens.

A Pentax * Series 300 f/1:4 ish
Sigma 100-300 f/1:4
Sigma 150-500

The first two get very high ratings in the various forums I've checked. The Sigma 150-500 rates a little lower but has the extra reach.

I'd appreciate any feedback from Pentax users who have any of the above.

Cheers

Kevin