I cant see how you wont get 300kw out of a Rb25de. You will need to spend some money on it. But it is possable.
In my old 31 (1987 S1 GX). i had a standard RB30e with 218XXXklm then put Extractors on it, standard catback with a cannon no muffers, POD, CAI, Stage 2 Cam, Port and Polish Standard comp. made 111.3rwkw on 97RON with 1 bottel of octane boost.
I only spent about 1200 on my Rb30 to make that much power. The rb30e come out with 114kw at the fly wheel. so i had a fear bit of a increase. and it still had more to go. Could have put a After market ECU in it and got it tuned. a big Catback. Pushed up the comp by heaps. change the fuel pump becasue you could feel it limiting the engine at high revs. It would have been a very fast single cam engine for its age.
so with the Twin Cam rb25 i cant see the probelm with 300kw engine. ECU, Big Cams, Big Comp, Port Polish, big zorst, and even abit of GAS for the track.........
Soon as i sell my 4WD and buy my GTS. im planing on building a fast Rb25de but i will run GAS for sure.
cheers Deano