400 DPS with your gear on a 6 minute parse is reasonable. Especially without AA damage. You could do better by knowing exactly how to pace yourself for the 6 minutes without going out of MP and getting full use of Fester (not having to sub it for Energy Drain for MP). That way you can sub in some Ruin II to make sure more of your Auto Attacks go off.
But why train that hard on a Dummy right? It sounds like you have the priority system all sorted out and can probably do good damage in real fights.