Seems we go from reading out loud, to reading in our heads (internally-vocalising), but you can continue and read without the internal-vocalisation. I can do it a bit, but under test conditions I only picked up about half of what I would do when I read to myself in my head.
Amazing how different people's headspaces are.
I can supress the vocalising with a bit of conscious effort but it's not the vocalising that limits my reading speed. It's all the rest that goes on in my mind that processes the information I just read. If I'm looking for some specific words, not vocalising is helpful but if I need to remember and understand the text I'm reading, I do vocalising as that doesn't impact the rest that goes on in my mind.
So I'm not a speedreader but it did help me to improve my glancing skills and if I need to I can count really fast now by visualizing the numbers turning into each other.
How do you articulate speech? With me, the concepts in my mind just turn into vocalized words. It's note even an effort, it just happens when I want to speak. Like my thoughts move the muscles in my arms. I don't know how and I am surprised that my line of thought rarely stumbles and doesn't produce the correct words. I think it should be some kind of effort to turn that wordless cloud of abstract thoughts and concepts into words but it just isn't.
I do have vocalization when I'm reading or when I'm preparing a text (like this one I'm just writing). But this is just to get the phrases and wordings the way I like them to be with the right effect.