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300 more #*$!ty links? I doubt it :)
"I paid for 150 PR 1-5 links, pointing to this page, with 3 rather targeted terms."
Those are not going to be natural links and by the sounds of it they'll be on a blog network. So great, just as I suspected more spam. PageRank shouldn't be much of a concern more so site relativity and quality.
4. Build higher quality links to your homepage and stay away from competitive SEO altogether.
...the websites were all legitimate, hand selected websites that were acquired.
It won't be long before one of my competitors, in my main niche, starts taking out competitors. They're dirty black hat scum bags and in the past 5 years haven't had a single drop in traffic, despite being involved in every link buying scheme I have ever seen, sabotaging adsense campaigns and just about every other underhand tactic. They're now at 500,000 visitors a day.
It sounds that for your experiment to work, it took links on 150 sites of a blog network to be able to do damage, right?
I guess your competitors are lazy, and it sounds like you are pretty hard working (after all, you built up the very extensive blog network), right?
Or would they first need to build up a network of sites to be able to sabotage someone else?
I apologize in advance if I am not understanding you. English isn't my first language; I am a product of the California Public Education System.