Mad Darts heads brought your combo up 20HP - 446 @ 6000
Mad Darts cam hurt the Dart/WCG combo - down 6 HP
Mad Dart also runs an SP and large tube open, so.............
Your heads with with SP, Open big tubes, MDs cam runs:
486 @ 6000
Use MDs heads as well - 516 @6000
Result
Your cam seems ok, your heads are not doing it - probably because your intake is crap and your headers are choking the whole deal.