I put a second 6000 into my 70 UkGal, and it took alot of juggling and moving corals, mainly becuase of 3 goniopora and Alveopora and I have now gone bare bottom. But it is sure worth it, that flow goes everywhere, I mean everywhere. It took a week before the bits floating around disappeared.
I have 1 dialled to min/min and one min/Max,
As roger says it depends on your setup, Soon I shall be going up to a 120.
Good Luck