Zuiko 50/1.8, six elements in four groups; Zuiko 50/1.4 seven elements in six groups. So, from the standpoint of contrast and flare control the 1.8 will perform better than the 1.4 because it has fewer internal surfaces and smaller diameter elements - 1.8 has six internal surfaces, the 1.4 has ten.
All other things being equal, the slower lens will have greater apparent sharpness-"crispness" if you will.
Yes, that's the theory. In my experience, the differences do exist, but are slight. Also, a lens such as the 50mm f2 Zuiko Macro should be complete crap with it's nine elements, but it is a very good lens.
"She's always out making pictures, She's always out making scenes.
She's always out the window, When it comes to making Dreams.
It's all mixed up, It's all mixed up, It's all mixed up."