You want to keep as much as possible, after all, you bought the live rock FOR the living things on it. However if you're cycling with live rock, or culturing it, dieoff is part of the process in either case. From my perspective, it's very hard to keep the polyps, featherduster worms, and other more "advanced" forms of live on the rock in great condition while curing or cycling with it. If you want to keep everything on it, then go with as much as 5-6 watts per gallon, keep in mind that's ideal, 3-4 would also be okay, but the higher the better.