As Ray N stated the bore is smaller to make it thicker for mechanical capacity as well as thermal handling characteristics. You do not need to overbore it in order to achieve more power. Fuel system upgrades (injectors, fuel reg, pump), exhaust upgrades (turbos like little backpressure and are inherently quieter), Turbocharger upgrades (higher capacity everybody likes t3/t4 hybrids for that displacement), Boost increases (custom burn chip or custom bpr) will easily fulfill your desire for more power. Putting it to the ground is the hard part maybe you can run nitto drag radials all the time but they wear quickly. It may be possible to adapt an AWD system out of a XC70 or V70R. A better breathing engine with a baseline high performance build will obviously produce more power than a stocker. Concentrate on the fundamentals of airflow increases and you will make substantial gains. Send the Head, Intake and Exhaust manifolds off to be extrude honed and ported thus smoothing the flow of air and reducing turbulence. Research camshaft replacement possibilities or even have them ground for more lift(in extreme cases). You always have the options of Nitrous Oxide, a well built system with basic safeguards will prevent catastrophic damage to your engine in case of a severe lean condition (use for racing only). Upgrade the plumbing (Stainless mandrel bent pipe is best) from the turbo through to the intake and get a better intercooler if available. When you pump big boost into an engine you have to have a good foundation. A better rotating assembly with forged I-beam rods, bulletproof (forged) pistons and high end rings. These can all be sourced through a competent machine shop or engine builder from US suppliers. Try Wiseco and JE for Pistons and Eagle or Carrillo for connecting rods. The valve guides and seals have to be made to tolerate high boost numbers as well. You can even have the builder or machinist custom make a stud girdle for the bottom end if your goals are really high numbers.