Wat?
TBH i would expect any decent tuner to tune pretty much anything you throw at them. Not just Haltechs. I would expect any tuner to tune PFC's. If they can't/won't then it's simple, we kill the batman.
But in all seriousness, if a tuner can't/won't tune haltechs in particular i would question their abilities.
but anyway this topic is getting out of hand. The question was what ECU for 400KW+ the simple answer is keep the nistune. Buying a PFC when you already have a Nistune makes no logical sense. Speak to your tuner about the top brands and what they like to work with/look into what other people are running. The fact is the majority of performance GTR's run one of the haltech variants these days and there is a reason for it. They are fantastic. But at the end of the day the question of budget is drawn up. Your budget will decide what you get.