Memory considerations, plus light-load CPU tests
It's inevitable the A6-3650 is going to be slower than the A8-3850. Look at it in isolation and with memory bandwidth the sole focus and it's not too great...but then neither is any AMD chip.
The PiFast test imposes a light load on the CPUs. Chips with the ability to increase single-core frequency above and beyond default levels do well here. The A6-3650 and Core i3-2100 don't have such inherent technology. It's clear that Intel's latest CPUs are simply better at these tasks.
And that thinking is corroborated with the light-load iTunes encoding test.
