To me heads cam and cr is the main trio of power, obviously you also need the appropriate intake exhaust etc.. to go a long with it.
Heads is basically the main potential (hp) that the rest is trying to bring out, so poorer flowing heads needs more cam and cr etc.. to get similar hp with better heads and should need less cam and cr etc..
So if you want smaller (within reason) cam (driveability) to reach a power goal then better heads are the key.