I have a few pairs of loudspeakers that are in use in various rooms. The Meadowlark Audio Heron hot rods are a 4ohm load with a sensitivity of 90dB while the Bohlender Graebener 520's are a 4 ohm load rated at 88dB. I have a pair of large DIY Legacy Focus clones (not really clones but similar in appearance using Eton drivers with Peerless 12" woofers). The sensitivity and ohm are unknown but were significantly more sensitive than the Von Schweikert VR4's they replaced. I'm picking up a pair of Triangle Stratos Lunas tomorrow with a sensitivity of 93dB.
With regards to how loud is loud enough? Oh, on occasion, I do like some music quite loud. Can you really listen to Rage Against the Machine any other way? Or the Red Hot Chile Peppers? Though I usually listen to jazz, both classic and modern and chill music or house music. These are all listened to at levels well above background but would not preclude conversation. Also note that different speakers reproduce sound in different ways. The BG's are dipole ribbon hybrids and close up, they sound like they aren't producing much sound but step back and the sound fills in and fills up the room. Thanks.