Some would be ok, some won't. Originally the 9920's were 9918's. They infact were underrated and BK found that they could easily run 20 without risk. I don't doubt that you could run a little more than that to be honest. I'm sure there are others that can be run more than rated for. The main thing I would worry about would probably be the caps. All I can say is don't do it with a Schulze :p.
...The main thing I would worry about would probably be the caps...
And for that you can just look at the voltage rating on the cap itself. For safety and lengevity, I would only go as high as 80% of the rating. Of course there are other components in there that can blow before the caps do...