The 25/10s are unlikely to produce your goal of 500 rwhp.
The std afms will run out of resolution well before 500 rwhp. It's not so much a case of restriction, but resolution. The PFC (and any ECU including the original for that matter) uses two 3d maps (one for timing, one for fuel injection). Each map uses load as the y axis as determined by the afm output.
OK, if you run out of resolution for load (ie the afms are beyond maximum resolution) you can only use one load value for both timing and fuel injection beyond this point. This means a compromise in power at best, and engine damage at worst. The cheaper RB25 afms will give you enough headroom for the 25/10s.
Don't get hung up on hp numbers - if you have a good low restrictive exhaust system (you didn't mention what you have) and tune to suit, then you will have a very responsive and quick GTR.