I'm of the opinion most tanks have way too muck rock so take my thoughts with a grain of salt(water).
The density of the rock is a factor. Ten pounds of Aquacultered rock is going to be half as large as quality imported rock because the imported rock is much more porous. The more porous rock will also have greater filtering capacity.
Your stocking levels are another issue. Typically corals add very limited bioload to a tank, with some exceptions. If you plan to heavily stock fish you'll need more rock. Problem results that there's so much rock that room for the fish/coral is decreased. Some people resolve that by putting rock in a sump or refugium.
The best choice IMO is to look at several pics of tanks, figure out what you like as far as looks go, and proceed from there. Personally I've found it easier to add more rock than remove rock in an existing tank.