Being a successful car journalist, Matt Farah has been able to get the hookup on modding his Ford Focus RS. It seems like he’s basically maxed out the stock turbo at this point, but just look at the huge gains his car made in the mid range. That’s a ton of usable performance!
Now, he quotes ~350whp, but remember RS’s need to be dynoed in front wheel drive, with the rear diff unplugged. Figure around 10% drivetrain loss for FWD and that shows around 380-390hp at the crank. Now figure around 20-25% drivetrain loss for AWD, and the peak power on the stock turbo (likely on 91 octane) is +/- 300awhp. Not too different from an STI, but please believe a bigger turbo will be a popular mod on the Focus RS for those wanting serious horsepower.