Rob, about the dubbing. Fact is that most Italian horror films were filmed with 2 different languages being spoken on set (nearly all Italian horror films had American or English lead actors to secure the film international distribution), so you'd have your main couple of actors speaking English and the rest speaking Italian, and on some of those films they didn't even record sound on set and recorded 100% of the sound in post production so it's all dubbed anyway.
The reason they are all released more widely in English rather than Italian even though they are Italian films is that they were being made mainly for overseas distribution. The Italians were really into "genre film making" at that time. If American westerns were a big success like they were in the 60s, Italy would churn out a bunch of spaghetti westerns cheaper & faster, and always more violent (because Europeans had alot more freedom in their film making, alot less conservative than the Americans) and sell them overseas, and whadya know - you've suddenly got all these Italian westerns like Fistful of Dollars, The Good The Bad & The Ugly etc making HEAPS in America. Hitchcock's thrillers were huge in America, so then Italy made similar styled films (their "giallo" films) but loaded in far more sex & violence. Then "Dawn of the Dead" becomes a huge hit, next thing there are a hundred Italian zombie films on the market, again with nastier violence and more sleaze than Dawn Of The Dead and the US films. So obviously the horror fanatics in America can't wait to go see these Italian zombie films which take it a step further.
Generally you'll find the videos will ALWAYS be in English no matter what country the movie was released in, unless it was Italy itself which'd be in Italian, or Germany also usually had everything dubbed into German. Every other country would be in English & subtitled usually. With the new DVD releases, alot of them are good enough to provide both Italian with English subtitles or English audio to choose from. Some only have the English audio though, and also for most of the films the English soundtrack is the main & original one anyway as the film was made for the English market in the first place. You just happen to have 50 Italian actors in the film speaking their own language on set.
It depends on the film which I prefer. Generally the pre-1975 films are better in Italian (except always have an English speaking lead character somewhere badly dubbed into Italian!), but the ones after that often only even have English soundtracks. I know that all the films Argento did between 1977-1985 (his most popular era) had English soundtracks even though some actors are obviously speaking Italian, but the films were originally made with English soundtracks. For that reason I prefer to watch "Deep Red" (1975) in Italian because the English dub is terrible and some scenes in the uncut one were never even dubbed and subtitled anyway. However, a film like Tenebrae (1982) or Suspiria (1977) were made with the intention of having English audio and if they even exist with Italian audio (never seen them in Italian), I am guessing it would be an Italian dub made AFTER the proper English one, just for the Italian market, even though the films are Italian themselves. That said though, I preferred watching The Bird With The Crystal Plumage (1970) in English, even though that was originally in Italian (and had only seen it in Italian with subtitles for YEARS before I bought the DVD) - because the 2 main actors are speaking English on set anyway and the story seems to have more momentum in the English dub.