If people are brave enough to turn up the boost high enough to make a 400hp dyno pull. Then that should be good enough, no matter what the motor. I bet there aren't many.
100hp increments above 300 seems cool. You could see who is where in the hierarchy when reading posts. Those guys that have made the 300 club already can get inspired to push just a little harder and make it to the next level, or the 500 level if they like..
280rwhp and 280 rwtq on a conservative Mustang dyno. The shop owner was blown away by my car even before I told him it made that power with an ebay "t3/t4", box (ebay) manifold and an ebay intercooler. This was at ~24 psi.