Perhaps the Dev could chime on on what a Difficulty of 8 would do. I would need to review the white paper in detail to know for sure.

If the POW is based on finding prime chains, moving from a 7 chain to a 8 chain is roughly 12 times more difficult. So if you were finding 12 coins a day, as soon as 8 is reached you will on average find 1/12 of that which is 1.

Same thing from 6 to 7 or 8 to 9.

With Primecoin 8-9 in many ways killed mining. It was simply impossible at a difficulty of 9+ to mine and fine primes with that chain length.

Dev thoughts?