Neil, thanks for your input. I am not a birder and have limited experience here. I do know 2 canon shooters one of which is a birder first and photographer second and the other photographer first. They both shoot canon and seem to get great shots. Complaints from them have waned after the 7d and mark III so I assumed focus was improved. I have learned that you can't entirely judge focus accuracy from a good photo. It is the percent of sharp photos that also matter. I read an interesting enews article from a non Nikon vendor. The photographer was touting a portrait lens lens with shallow DOF. After he acquires eye focus w fstop 2 he slowly leans forward and backward and gets a few sharp shots out of 50. I thought wow, I have better than 50 50 hit rate with my 50 1.4 and 85 1.8 af old lenses. I think a lot has to do with our expectations.
"Cameras and lenses are simply tools to place our unique vision on film. Concentrate on equipment and you'll take technically good photographs. Concentrate on seeing the light's magic colors and your images will stir the soul." Jack Dykinga