this mod is spot on for rb20/25's although i would mount throttle body directly onto manifold to increase throttle response further.
there will be no lean-out in runners because,
pressure in system is equal whether at compressor outlet, intercooler or inlet runner.
compressed air reacts like liquid/hydraulics therefore if each inlet runner is of equal length and pressure is the same each runner will flow equally.
so the big gains will come from your tuner putting more fuel into the engine earlier, 2m less plumbing adds to a ton of response, reducing heat soak and increasing turbo efficency.