It's not so much the speeds that differ, but the micro-architecture. The big cores are typically out-of-order cores with a large amount of cache, to get as many

It's not so much the speeds that differ, but the micro-architecture. The big cores are typically out-of-order cores with a large amount of cache, to get as many instructions as possible per cycle. The SMALL cores are in-order cores with a small amount of cache. These have a lower IPC, but they also use much less energy per instruction compared to the big cores.