[I tried to find a complex answer to this thing I’ve been thinking about but didn’t find anything, so sorry if this was discussed before. I am spinning articles using TBS. I usually don’t use all the advanced spinning techniques and just spin the words and phrases to hit uniqueness ranging from 50 to 65 percent. My main goal is to make quality articles that make complete sense even in spun versions. And as I am only sending them manually to article directories, using one article maybe five times, I only add one synonym to every word/phrase I replace. My question is, is the uniqueness I create and one synonym for a word/phrase enough when you take into account how and in what quantity I use the spun articles?]
I think some folks are not reading your OP before replying. You are asking how unique your spun articles need to be to avoid the duplicate content filter, right?
Google is pretty good at detecting synonym replacement. If you are just doing synonym replacement then you are likely to have all but one of your articles filtered from the SERP for a given keyword. You should rewrite the sentence at least once as well as doing synonym replacement.
I have never seen evidence that suggests they are any less powerful in passing PageRank or Trust.
There is no duplicate content penalty, it only gets filtered in the SERP post query. If a page gets de-indexed it is for another reason (i.e. copyright violation), not for simply being duplicate content