FI is the only way to increase to that level. The MREV2 is a great boost, alongside the plenum spacer, but to be fair, you're not going to pull 30 bhp from adding a Y pipe, decats and exhaust.
Hence I chose NOS....
I'm not fully aware of the true flywheel calculation you have there, but my understanding is you add the powertrain loss of 17%. So in effect your 257 is 300.69bhp at the fly. (Someone correct me if I'm wrong).
Despite spending thousands on NA mods I've only achieved 263 at the hubs. In hindsight with all the NA mods and the NOS I could have gone for a wicked SC setup.
Maybe that's a project for next year after selling all the mods and NOS with some extra cash in the pot?
Oh and to add... the 296bhp which Nissan quote is inflated....!