Airbox and injectors are not limiting to 300rwkw.
Airbox will do 400rwkw, it's been proven time over. $700 saved.
Stock piping is fine, doesn't look great, but stops compressor surge. $400 saved
Injectors will do around 300-320rwkw, which is what -7s will make max. So you save not needing rail/injectors/FPR etc. $1400 saved
Intercooler is also totally fine. $1000 saved
So $3500 saved already from things you simply do not need, and never will