why would you run a piggy back on a GTR?
i used to run an emanage ultimate - it was good for $500 and around 220-230kw BUT for anything above that you would want a standalone ECU.
personally, i wouldnt go for a power FC unless it was a bargain buy at under $1000. for the extra $600 i'd go for a link or vipec in terms of bang for buck. support for the vipec is direct with its creator, ray hall on the vipec website.
its simple to use and the add-on features are great (e.g. knock sensor, wideband for the auto-tune feature or logging, oil temp/pressure etc, boost control). and the help file ACTUALLY helps.