GizmoChina has a very clear post explaining what I tried to do here and here and here: Why is eight-core (octa-core) still slow on cell phones?
Memory bandwidth is actually more crucial.
Smart phones and tablets are all SOC, meaning the graphics core is integrated, sharing memory bandwidth with the CPU, with no independent memory. And resolution is getting better for phones and tablets, this puts a great demand on memory bandwidth.
Programs need to run inside the internal memory. If the processor is quick, and the memory access speed can not keep up, the system will still be slow. And as resolution increases, so will the demand on memory bandwidth.
When memory bandwidth is not enough and resolution is too high, no matter how fast the processor is the system will still be slow.
See the entire post — and bookmark it for future reference.