The size difference between the big and LITTLE cores is really large!
I though it'd be around 2x larger, but a Cortex A15 cluster is actually >4x larger than a Cortex A7 cluster.
The difference is smaller with the A53 because it's ~40% larger than the A7.
So if we assume that a 2-core cluster is ~60% the size of a 4-core cluster (the "MP core glue" probably can't be halved), then using Samsung's 20nm a 8-core Cortex A53 would occupy 9.16mm^2 whereas a 2*A53 + 2*A57 would occupy 11.81mm^2.
The chinese SoC makers like HiSilicon and MediaTek have been sacrificing single-threaded performance for a measly 2.5-3mm^2...