I think I'm more comfortable saying, "What the Bible says, is said with God's authority" or "God speaks through the biblical authors" -- rather than saying all of Scripture is spoken with His voice. This is probably more a nitpicky stylistic or literary thing than a theological thing. In the Old Testament, obviously, God speaks directly in a lot of places, He appearing and speaking as a person, for example when He's speaking to Moses. With the prophets, it's possible to say, "the prophet Jeremiah says," but what the prophet Jeremiah says is appended with "thus sayeth the Lord" -- indicating that it is God speaking through Jeremiah. With other books -- including the New Testament -- they are different literary genres. I don't feel comfortable saying, for example, "God is writing a history," but rather "Luke is writing a history under God's inspiration." Do the words have the inspiration, authenticity, and authority of God? Yes, sure. But is it God speaking as a person or character? No, not really.