IP space usage does not effect SEO much, if at all.
I've had 5 sites on the front page at the same time for the same term, ALL on the same IP. This was for a good sized single word, porn niche. I currently have a bunch of sites placed on front pages for a number of competitive adult terms, all hosted on same 4 IP's.
Blogger.com has thousands and thousands of well ranked sites all on its few IPs. Blogspot.com and tumblr do as well. i can name them all day long.
its a new age, stop believing everything you read on the internet about SEO.
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