Uniform blocks : Optimal qualifiers

Greetings,

I'm currently playing with OpenGL ES 3.0 and I'm wondering if Mali (>= T6xx) drivers can perform interesting optimisations based on the chosen layout qualifier applied to Interface Blocks  ? (shared, packed, std140, row_major, column_major)

The fact that Std140 avoids pinging the OpenGL implementation, about the data layout, makes me wonder if there's any reason to choose another layout qualifier.

• If a uniform block is shared between multiple programs, is it useful to choose shared ? Even though the uniform block will just get its data from a Uniform Buffer Object ?
• Does packed really provides useful memory optimisations for OpenGL programs ?