I did it once at 180CFS, and will never do it again. I think 250CFS would be my cut-off. You can still get down it at 180 but it really isn't worth it. However, Pine Creek was still somewhat fun at that level. I would get out after triple drop and walk back up and run it a few times to make it worthwhile. I only did this because I was bored and live 10 minutes from it.
Depends on why you're there. You can scrape down just about anything with almost no water. 300 is my threshold for the Numbers. FYI, I tend to be willing to run things much lower than most people I know would ever even consider it.