I recently purchased an 8-9" royal panaque, along with a 10" hoplias (wolf fish), for $100. The panaque is probably four-five inches across, without his fins spread out.
Him along with my new wolf fish:
Taking a break from wood:
Yeah, yeah, another side shot:
Within the next 24 hours, I'll have some better shots of him. I will get some full body shots, face on, up-close of his mouth, and I'll try to get a picture of him swimming, or upside down and chewing on wood.