Think of it as a sliding scale. If your site is a complete dupe of another site it will be heavilly penalized. If your site is 100% original exclusive text it will be most favored. If your site is mostly original text supplemented with quality nonexclusive content it will fall in the middle.
Keep in mind, most RSS feeds are very badly written. They contain errors, typos, mispells, illegal terms, broken links and many other problems. So when you rely on a feed, not only are you taking a hit for duplication, you are also accepting all the flaws and fuckups of the original feed. The person writing 500 feed posts is typically not going to craft the best text or anything close to the quality of a professional seo text writer.
So, what's better? A+ text that is also original or C- text that is also duplicate text?
If you want very high quality original text:
www.EngineFood.com
If you want to keep costs down, at least read the feeds carefully.
Best of luck either way ;)