I've increased the reading speed in OS X's Speech Preferences (and changed the voice from the default) but when I ask Logos to Read Aloud it still reads with the default voice at the standard (rather slow in my opinion) voice.
All other OS X apps that use the OS X text services follow the preferences specified in the Speech Prefs settings so this is a bug.
See also my report about the too-short pauses between sentences (which is a Logos but, not an OS X speech service bug):
