I'm generally a slow reader, I 'spot' each word individually and subvocalise - that's the most enjoyable reading mode for me. It gives me more time to detail the mental image, and savour the emotional ride.
For dull reading (e.g. at work) I can 'spot' word groups, and not vocalise in order to read faster; but it's a continual effort, and not pleasant for me.
Dictator is a freeware app for reading Gutenberg texts that can also be used to test reading speed.
"Dictator provides an alternative approach called Rapid Serial Visual Presentation (RSVP) in which words are displayed consecutively in the same place at a user-controllable rate."