[iOS] Is a mostly opaque texture faster to alpha blend than a mostly translucent one?

I'm developing a GUI for an iOS game.

Let's say I have a circular button texture. Most of its pixels have alpha=0 (outside the circle) or alpha=255 (inside the circle). The only translucent pixels (1<alpha<255) are along the edge where it's anti-aliased.

Compare this to another button texture where the entire button is translucent (alpha=192).

Is there any performance difference between the two? Is the system smart enough to realize it doesn't have to calculate alpha blending if the source alpha is 0 or 255?

(edit: fixed bug caused by '<' characters)