The 206kw quoted by Nissan is not rwkw but flywheel kw. Your R34 is probably a little low and you are absolutely correct in that different dyno's produce different power figures. As an example I have Nismo FMIC, Nismo Injectors, Nismo fuel pump, Nismo reg, PFC, Z32 afm, hks 2535, Tomei cams, Apexi pod filter and full exhaust system from turbo back and produce 210 rwkw @ .6 bar on a Mainline dyno but 247 rwkw on a Dyno Dynamics dyno. It's all in how they set up the dyno. Like the other guys say, get a good FMIC and ecu and then you end up like the rest of us ..... just feeding the addiction!
cheers and enjoy the ride
Muz