Which leads one to ask... to those who say " I have to have really fast AF for BiFs...." "What's wrong with you? "
The biggest issue with BiFs is my skill win tracking them in the viewfinder. The AF of the camera comes into play at times, but is not the critical element.
Met a guy from Ontario Outdoors shooting an owl in AP a few years ago. He was using high end Canon gear. I saw his published pictures, and I saw one of his prints sell in the Visitors centre, but in the magazine and and as 16x20 print, no one cared that it was bit soft. Sometimes the best gear doesn't get you a clean shot. I have no doubt a Pentax would have been worse. But I also have no doubt, if I'd been in the same location and nailed the shot with my K-1 and A-400, my images would have been a lot better. I guess I'm just a gambler at heart.
I'm willing to gamble that the resolution limitations of fast AF cameras will work in my favour, more than slower AF will mean I don't get images. The one thing that never gets mentioned discussing fast AF, is the price you pay in resolution to get it. I want the image, and the best possible resolution. In going for a fast AF camera, you've already conceded the resolution part.