I feel I can't really set a firm numbered goal for reviews done each week since I don't want to miss that number by having a 'bad brain' day, but I consider anything three or above to be a decent out put. The reviews are between 250 and 400 words each (an average of 325 words) and three reviews would mean I write 975 words each week that I finish three reviews. I am doing better since we moved. For example, I submitted a total of three reviews in May, four in June, ten (!) in July and seven in August. (I keep a spreadsheet tracking books from the moment they hit my door until I submit the review.) So far in September I have done seven and hope to get at least three more finished off by Sunday the 30th. I have hope October will be better (maybe at least twelve reviews total) since I will be writing on reviews six days a week.
The increase isn't all about the move, we also bought a new laptop for me that does not highlight and delete text willy-nilly (which I think was originally written 'will he or nil he'). The writing goes a lot faster now. At full speed I type from my head pretty quickly, but only if the words stay on the document! (On a whim I took an online typing test that clocked me at 55 wpm when I am copying a text. When I am just writing from my brain, I do about 75 wpm.)
A rule of thumb in fiction writing is that each page has about 250 words. That means on a decent week I write almost four pages of reviews (edited work.) I would guess my rough drafts run anywhere from a basic outline of 100 words to 500 words when I really get umm... verbose.
The lower-output writers I've been learning about often try for a page or two a day of unedited text. In the past when writing fiction, my unedited first swath tends to be pretty long-winded. I don't think it will be a problem to write at least one page, especially when I am just getting down my first thoughts. Later when I am actually tightening up the story and adding some plot work I imagine things may slow a bit.
Rather than shoot for specific numbers, I will keep my goal to try six out of seven days (with one day off for messing around and doing other stuff).
(The image above is from the The History Center in Tompkins County located in Ithaka, New York)