You are challenging yourself to the max here (so to speak) because it is very hard to track these little birds in flight and keep focus on them even with a 1D series Canon body. You did pretty well on the Nuthatch. The image is suffering from a large crop as well I suspect.

I agree with neuro that a little more depth of filed might help but you need all the shutter speed possible because the wing tips are moving so fast.

Practicing will definitely help your skills and if you can find some bigger, slower targets (like maybe Gulls) you will get better results to start out with.

I usually use the center AF point only and adjust the tracking sensitivity a little slower than average so the camera won't jump to the background so quick. Also I try to watch and anticipate the flight path, it's easier to focus on the target as it approaches by pre-focusing at something the same distance away, then attempt to hold the AF point on the bird until you see the shot you want and then start firing.

I am not familiar with the 60D and it's adjustment features but your lens will definitely focus and track better without the 1.4 converter. So if you can get closer the images will be better too.