You probably don't want to hear this but there aren't any real worthwhile power upgrades out there for a NA 850. You're really better off just doing suspension and braking upgrades. But you're right, if you really want to increase HP and torque on a NA 850, it's going to cost you a lot of time and money which is why I, as well as many others, recommend you to not bother. EA has been known to inflate HP and torque gains which is why I suggest to many people who ask to consider shopping elsewhere. Good tuner companies don't need to make outrageous claims to sell their products.