Stage 2 on a GD means one thing at its core: a 3-inch turbo-back or catted downpipe plus a tune. The stock downpipe is the biggest single restriction on the car; removing it lets the stock turbo reach its targets with far less exhaust backpressure and drive-pressure. Everything else is supporting cast.
The right order: downpipe and protune together (never a downpipe on the stock map — boost creep and knock), then supporting mods as budget allows: turbo inlet, quality cat-back for sound, and a top-mount only if you're heat-soaking at the track. A fuel pump is cheap insurance at this level and mandatory beyond it.
Real numbers: a healthy Stage 2 WRX (TD04) lands around 240-260 whp and 280+ wtq on 93 octane. An STI (VF39/VF48) runs roughly 280-300 whp. The torque curve matters more than the peak — a GD at Stage 2 pulls from 3,000 rpm in a way stock cars never do.
What NOT to do at Stage 2: crank boost past the tuner's targets, run bargain e-tunes from unknown sellers, or add a bigger intercooler and intake without retuning. The EJ's ringlands have a reputation for a reason — and the reason is almost always heat plus knock from someone chasing one more psi.
Tuning changes engine behavior. Numbers here are typical, not guaranteed — your fuel, climate, and hardware matter, and a professional calibration for your specific car always beats a generic map.