My stream of consciousness consists of words. So, in any given day, how many words do I think? Word processors generally have functions to report the word count for a given document, but my brain has no such function.
wrong answer
Good answer.
ETA: good answer.
First, I’d challenge the premise: I bet you really don’t think continuously in words; that’s just an illusion your brain is presenting you.
But let’s assume that you’re rehearsing a speech, reading, writing an SDMB post, or some other verbal activity all day, and hence really are maintaining a stream of words (in addition to whatever other cogitating you’re doing).
Assuming you think word streams at about the same speed you speak them, and that you’re an average American English speaker, that’s approximately 150 words per minute. Maintain that for 24 hours and you get around 215,000 words.
Your mileage will vary a lot: you’re probably not doing this for 24 hours, and speaking rates vary a lot across professions, cultures, circumstances, and geographic regions. Speech can be understood at well over 200 WPM, and I’ve read claims that most people can follow 400WPM with some difficulty.
And then there’s that illusion thing again; Note that the speaking rates above are well below the fastest reading rates. There’s a ton of controversy about whether extremely fast readers (1200 WPM and the like) are actually reading or just skimming, but there definitely exist people who can read with full comprehension at 700 or 800 words per minute. The trick here is that they’re not actually reading words at all; their brains seem to be providing them groups or words, phrases, or even whole sentences as “lumps” of pre-processed meaning. They’re not conscious of each individual word going by.
It’s extremely likely that even the verbal parts of our thought processes are using a similar shorthand: you think you’re thinking sentences, but instead you’re just getting nutritious lumps o’ meaning. If we make the assumption that this is similar to speed reading (and mind you, we’re leaping off the Cliffs of Speculation into the Ocean of Wild Guesses at this point), that would get you to a rate of a little more than a million words in that same 24 hour period.
So that comes out to… what… 10 actual wpm or so? 
At least seven.
Perhaps even eight.