EM-5 with four thirds 300mm
My experience with worst focusing mft lens 50-200 SWD + EC 20 so far is,
focal frame/point may not be necessarily smallest focal frame/point bit just to cover major part of bird. Be it 5x to 14x just don't give in steadiness if you see focused image in VF as camera takes final call on best focus point after that brief cycle. Key is to hold camera steady till then.
Off course it is bit early observation on my part. Here is hand held example exif will tell balance of it..
|Nowhere by Nanard 92|
from The Illusion of Depth and Distance
|Green Tomato by lim yau tong|
from Growing Fruit