Hi,
Check the answer of Cyrus Shepard on this question: http://moz.com/community/q/are-cdn-s-good-or-bad-for-seo-edmonton-web - I fear it will be hard to find other quantified data.
"We've done a lot of studies here at Moz and what we've found is this:
- There does seem to be a slight correlation between site speed and rankings (keep in mind that correlation is not causation)
- Our studies have not found a relationship between CDNs and higher rankings.
So the evidence would seem to suggest that CDNs can help your website speed, and it's possible to help your rankings, simply using a CDN by itself is no guarantee."
Hope this helps,
Dirk