I tried two samples: Willa Cather 'The Professor's House' I got 300-350 words per minute. That includes going back to re-read the first paragraph because it didn't really sink in the first time. JFK's inaugural address I read at 400 wpm, because it was easier to follow. I suppose it was designed to be understood by an audience who couldn't go back and check the paragraph.
I'm not a fast reader. I think on extended prose I'd be a lot slower than that.