From researching on Google I found this. To be clear this is for the upcoming U.S. Model.

*ahem*

The Impreza WRX STi receives a major engine upgrade over the standard WRX, including a strengthened block, molybdenum-coated pistons for reduced friction and forged conrods, plus an enlarged turbocharger (delivering 17.5 psi of boost rather than 14.2 for the standard WRX) and intercooler, for a total of 276 horsepower (closer to 320) at 6400 rpm and 275 lb-ft of torque at 4000 rpm. Upgraded Brembo brakes - 12.8 (325.1mm) inch rotors in the front and 12.4 (315mm) inchers in the rear - and suspension, improved chassis rigidity, the 17 inch gold wheels, 6-speed gearbox, slightly wider track and foglamp covers differentiate the STi from the WRX. Combine this with the wider tires, stiffer chassis and stiffer suspension and the STi becomes a near-perfect driving machine, with awesome grip and minimal body-roll.

In the end, the WRX STi brakes, corners and accelerates better than the WRX, provides similar straight-line performance to its predecessor even with the added weight, and still costs a reasonable amount of money, well at least in Japan. Compared to the Evo 7, the STi is a bit more sluggish, with a heavier gearchange and softer throttle response and brake pedal but its still very potent compared to anything else on the road. On the other hand, its suspension is more capable to absorb all sorts of bumps. Understeer is slightly present, but the STi always ends up going where it's pointed, with its awd system and massive grip. A better and more comfortable daily driver than the Evo, the Impreza WRX STi is a superb machine and maybe even a wonderful bargain.

And there it is.