Is there more than a doubling of the shader costs if using translucency?

Development Rendering
1

Hello,

if I have two materials on planes in a row and the first one is translucent, is the resulting shader cost then just the shader cost of the first material plus the shader cost of the second material? Or are there more “invisible” costs? And a second question: do translucent materials have the same cost like masked materials at pixels where the opacity is 0 respectively the opacity mask is 0?

Thank you,

Thilo