Bingo. AEG should be limited to 400fps PERIOD, semi or not. If the user has an MP5K to use while stalking around or on patrol and a 450fps M14 on their back for occasional use, I've ZERO problem with that, they will actually gain more respect from me. Guys like Mason can use an M14 up to 450fps as a primary and get no complaints from anyone, because he's always on the flanks or near the rear to reinforce the front. Is the way he plays, and is the experience he has. And he's earned the trust from everyone to use that type of gun. Noobs with high powered AEGs, or even vets that are used to more than one BB in the air at a time, moving to an AEG that is over 450fps and swearing to use semi only all the time tend to forget that they are trying to run with the sniper role when under stress, and end up bouncing quite a few BBs off a guy at shorter ranges than they'd understand to be part of the sniper's creed bs.
While I'd never use or set up for myself an AEG as a sniper rifle, I'm sure I'm one of the few that'd get the full go ahead to use a 450fps+ M14 or such, just because I like watching where my single round goes, then compensate for the next shot. Add to that my comfort zone for shooting someone during a game (teammates don't count).