Both of these will slow you down to the point in which you find that you can't read any faster than you can speak. Speech is a relatively slow activity; for most, the average speed is about 250 WPM (words per minute).
Reading should be an activity which involves only the eyes and the brain. Vocalization ties reading to actual speaking. Try to think of reading as if you were looking at a landscape, a panorama of ideas, rather than looking at the rocks at your feet.