As for ratio, the SVX is 3.54 final drive. A WRX 5MT in the SVX will be a 3.90 final drive. Any 6MT swap will be a 3.90 final drive. No matter what you will be increasing the final drive ratio and the RPMS that you cruise at on the highway. Even worse would be the 4.44 auto swap.
Final drive on UK cars is 3.70, not sure about mainland European cars.
