For some reason, I couldn't search effectively on these terms, so I decided to back up and load 10.10.3. Well, Preview is indeed better, but still un-usable. On a scale from 0-100, it goes from 3 to 7. It opens my file (PDF) better, but as soon as I zoom in, one of the cores goes to 100% CPU usage, and stays there, making any subsequent re-sizes or moves incredibly difficult. Yes, I filed a bug report on this, and I even gave them the file for a benchmark. There's nothing wrong with the file, it behaved perfectly in Preview pre-Yosemite. Oh well.