I specialize in query letters to literary agents and editors and have around an eighty percent, "request the full manuscript" rate. I've been published by Berkley, St. Martin's Press, Avon, Lyons, and Alpha Books, among others.
Getting a request for a full manuscript is no guarantee that you'll get an agent or editor to take you on, but at least you'll have a fighting chance. Your work will speak for itself -- and isn't that really all you want? Just tht chance?