Up to 8 of these now which is probably as far as I will go. All are running happily at max speed and completely stable.

Impressive....are you running at max frequency? Do you have core voltage maxed out as well?
No way he's running max clocks AND maxed voltage...regulator would definitely blow up or shut down due to over-current protection. Definitely don't recommend running these at max clock, but running one of these at max clock this stable is impressive...8 all one the same hub...thats crazy!