The limiting factor in your spec is undoubtedly that turbine housing and potentially also your boost control. The .48AR turbine housing is tiny and restricts the engine massively from 5000rpm upwards. If you want more top end power, fit the .63 to extend the powerband upwards, but for the best power you really need some form of programmable boost control, ideally air injectors as that gives us good rpm control too so we can push the turbine at high speeds.

Ultimately though, its all down to how you want to drive the vehicle. Do you want big slugs of low end torque so you can shift at pretty low rpm or do you want to push her to the rev limiter every change and need a more linear power delivery due to the minimal weight of the vehicle?