Hi Pete,
Andy nails most things so ill just talk about the "how different part".
Google is very good at identifying the structure of a sentence and determining its meaning. To simplify things I always look at it like this
"It is warm" is the same as "It is hot"
changing text like this and hoping its unique is asking for trouble. Instead try to write as if you are a different personality appealing to a different type of person within the context of the site.
Site: 1 Mr technical writes the content for this site. Your all about the technical features, why they outshine the other specifications and why thats good.
Site 2: Mr indulgent writes for this site, he is less concerned with the technical and is all about actually using the product. He talks about the ease of use and how great if feels to use etc.
Site 3: Mr in the middle, he has a descent amount of respect for the technical elements and mentions them, and has a more speculative approach of explaining why this would be good.
These three personalities all talk very differently, use a different pool of words, create these persona's and be them as you write. This will give you the base difference to make identical information very different.
To combat similar products, my approach has been to not try to distinguish them too much but to engage with the similar products and talk about them. For example product A is the same as product B except product B has a special paint on it that makes it look good so it costs more. So product A is all about value, its the cheapest in the range so great value for money, affordable but with all the necessary perks. Product B is luxurious, not only does it have everything product A has but looks dang good and is a real head turner.
This approach allows you include all the important content needed to get the word count up and make it a good page but present in a way that is very different.
Ignore this response