The experiment was run from the five countries where Tor is most popular; the USA, UK, Germany, France and Russia, and found that traffic from the USA and UK was far harder to crack. (The Silver Lining In This)
https://nakedsecurity.sophos.com/2016/10/05/unmasking-tor-users-with-dns/
I mask my DNS queries by with DNSCrypt...ran by OpenDNS...
For those of you interested, DNSCrypt 0.0.6
Basically, it encrypts your DNS queries and as a fallback in case of server issues, will even use TCP (although it's slower) to issue DNS queries over port 443. I'm sure it's not entirely NSA-proof...but it's one of those tools that gives me a bit of piece of mind when I'm running windows.
If exit-nodes ran this, as well as everyone ON the Tor network, I wonder if it would make this sort of correlation obsolete.