How much power do I actually need? Not much it seems, the quest for power is just a want IMHO.
It seems 4070hp is pretty much the sweet spot for street use depending upon the weight of the bike, rider, passenger, gear etc. The heavier and less nimble the bike,... the more power you'll "need" vs a lighter more agile bike... Any more is just a luxury purchase to satisfy "wants". Simple as that.