Re: Chip by chip.
This is AFAIK not possible currently without theoretical electron microscopes (or hardware flaws, which have not yet been discovered/published).
The chips have "secure enclaves", and thus if powered/used, even on a seperate board, will (since the previous 2008 update to the flaw) secure erase the *keys* if too many attempts are made. As we are talking about data inside the CPU/RAM and encrypted, you'd need to both dump it (without triggering the erasure, or damaging the chip) and decrypt it (how much GPU/CPU power do you have).
If Apple have designed the chip correctly, there's no feasible way to get to the data currently.