My tank cycled in a matter of days when I put in about a 0.75 lbs per gallon live rock.
I would be a bit wary of using too much dead rock though. From what I understand, it will quickly colonize with nitrogen cycle bacteria, but the bacteria inside the rock that fixes phosphorus doesn't migrate over too well.
When the rock is fresh from the ocean, it has been colonized starting with a piece of dead coral and grows over time to become the large rock, with its bacteria evolving along the way. This gives is different strata of bacteria, and you cannot just transfer that over by adding live rock in with it.
I definately used a good amount of dead rock in my tank, but just wanted to state that it isn't ever going to be the equivelant of live rock that has never been killed off.
Thats my understanding of it anyway. Don knows a hell of a lot more than I do about reef systems though, so forgive me if I'm mistaken.