About 5% of calf tails are truly suitable for dry fly wings. You need to look for straight hair with a nice tip. When you find a good one there is few things better, it becomes very easy to tie with and produces a much better fly.
For larger flies more calf tails will be usable because of the wing size the slightly kinky hair is less noticable.
I use some of the real kinky hair that does not have a mean curve at the tips for streamers.

Any calf tail that have a curve is going to be almost useless, most so if it near the tip.

We switch to calf body hair on small dry flies around a 16 and smaller, but you need to makre sure that the hair does not curve or else it will not tie well.
We also use calf body hair for most parachute posts. It has gotten better feedback in visibility and durability.

For large Wulffs (sometimes 10's but all 8's & larger) I have been using bucktail like Lee Wulff used, it produces a never nice wing but does require a large bunch of hair since the tips are so much finer then the butts. Like calf hair it does require selection not every tail makes a good fly.

The trick most of the time is the material selection, even the best tyers can't tie a good fly with material not suited for the application.

Joe Fox