There's a lot of misconceptions regarding a "duplicate content penalty". This is due to the fact that many discussions giving advice are regarding completely different topics that all use the same terms. Unique content and duplicate content are applied in different ways depending on the specific topic being discussed. When reading through articles and threads on the various topics, it's easy to make the mistake that they all apply universally, but that isn't the case. Whether you're better off using absolutely original content, unique content, spun content, duplicate content, or any combination of those will depend on what you're actually doing with the content.
Making sure you're articles pass copyscape is something you need to do when you're submitting articles to directories such as Associated Content, Ezinearticles, etc. Most of the better article directories won't accept duplicate content so in that situation duplicate content becomes a big issue, but that has nothing to do with Google caring about it.
Unless they receive a DMCA complaint, Google isn't really concerned about whether you're content passes copyscape. If you have 100% the same content as another site, and then you do a better job promoting the site, building backlinks, etc. then it's possible for your page to move higher than the original page in the SERP.
What google wants is for the individual pages on your website to have unique content in relationship to the other pages on the same site. The purpose of that is to prevent you from making many duplicate pages changing just the name, title, description, etc. in order to target different keywords. It's kind of a similar issue as keyword stuffing and can potentially penalize your pages.
Here are several other threads discussing the same topic in more detail:
How Does Big G treat spun articles?
What are the risks of 'spinning' content?
How does google determines duplicate content
Guide - Duplicate Content - Myths & Facts
SEO myths and reality
do any of you guys just not give a shit and blatanty copy content from wherever you want
Posting the same article to 1000's directories - good for backlinks or not?
No Such thing as duplicate content - Revealed
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To answer your specific question regarding using that content in your blogs, 66% is probably fine for Google as long as you're not using it to create multiple pages all on the same domain. Depending on the purpose of your blog pages you could probably be fine even if it was less unique than that. If you wanted to use that same content to submit to top article directories then that same article would most certainly be rejected as duplicate content.
As far as creating an engaging website that'll do well in the serps, AND entice visitors to continue returning to your site and recommending it to there friends then here's a fairly decent template for doing so. Create your main website with many pages with fairly original content, you can also have a few pages with non-original content if it adds value to the overall site. Create some quality unique articles or spun articles to submit to the top article directories with backlinks to your main site. Submit those same articles after they've been accepted to the top directories and submit them to other directory sites that aren't so concerned with duplicate content with backlinks to either your main site or to the articles you made on the top directories. Choose some of those articles from your main site and some of the better ones from the article sites and submit them to multiple blog sites with backlinks to your main site and some with backlinks to the article sites. It's actually better for many of the blog and article sites to actually be exact copies with a citation giving credit to the article on your site or the article on the other directories. If you do that then you should end up with all that content getting indexed in such a way that it all leads to your main site being the authority for that content.
You can do the same thing even if you have no original content on your site. The main difference for SEO will be the fact that for duplicate content other websites are also doing basically the same thing and so you're competing with them for the same content in the index. Even in that case you can still outrank them for the same content, it'll just take a more work.
(I didn't mention all the other SEO factors and backlink building you should also do since the topic of your thread is regarding just the content.)