Because you're interested in cone speakers only, my experiences are only half usefull to you since I own a hybrid cone/ribbon design. Efficiency is low, due to the closed housing for the woofer and the low efficiency of the ribbon. The low-end is among the fastest and best controlled I've ever encountered. At first you think there's hardly any low-end, but baby, there sure is. So my experience suggests that the lower the efficiency, the faster the sound is.
