Factory ECU has decent boost control which the tuner can manage with the tuning software (PCMTEC, HP Tuners, etc). So if you are paying for a tune you shouldn't need to spend anything on boost control hardware. Factory FG turbo tops out around 320kw. It is a good, responsive turbo on the Barra though, so if you shoot for more power and go bigger you will trade off a bit of response on the street so depends what you want to use the car for. Edit: posted same time as Keith but same same. I should have said I was talking 98 not E85