Tamron 150-600 SIF Photo
Just a Squirrel In Flight example taken with the Tamron 150-600 @ 150mm F5. No issues with focus tracking...and these little buggers move pretty quick. It's about a 75% crop and straight out of camera.
I have been using this lens for around a month and really enjoying it. Haven't missed the 300 F4 AFS it replaced at all.