Click here Version: 6.25.1.9091 (thank you CalS for providing this link)
Click on the "Download" button at the top right
It may download "OperaSetup.exe" first, but don't run it, and simply ignore it, it'll eventually download the older version
Run the install
You'll now have both versions available to you
Personally, I'm going to keep both versions active so I can check in on the new version periodically to see if they're changed anything.