One thing to keep in mind: when shooting at longer distances, AF speed is almost a non-factor, since the focusing does not vary all that much at long ranges. If the lens is focused at 65 feet, and a football play moves toward the hashmark to 45 feet from you, the focus movement really is not all that extreme. Same with things like auto or horse racing on oval tracks, when shooting from the grandstands...the focused distance is always in that just-short-of-infinity-focus range, where .035 millimeters' worth of focusing ring travel represents 40 feet of distance. Also, if the action is moving parallel to the camera position, focus distance does not change a huge amount, typically, so absolute AF speed is often not super-critical. With that said, it helps to be pre-focused on the right general area before a shot opportunity; don't expect to be able to rack focus from 15 feet to 155 feet in 1/10 second, with reliability and dependability,shot after shot. I learned this lesson with one of the most dog-slow Nikkors of the modern era, the original 80-400mm VR-Nikkor....ohhhh, what a doggy focuser it is when it needs to seek out a new target! But, when it's been pre-focused, at longer distances, it can follow NCAA running backs reliably on an old, weak AF camera (Nikon D1 or Nikon D70).