For grins..
I took what we know as reasonable top speed estimates for a K1600 GT of 155MPH, then using several online calculators reversed out what the Cd (coefficient of drag) is by taking the known frontal area (I measured my bike) and known weight (being kind at 950 pounds all in) and looked for a Cd number by targeting approx wheel HP (138 Wheel HP). If that sounds reasonable, then I looked for what those derived numbers mean for HP requirements to hit 170MPH.
Frontal Area = 9.135 ft^2 - I physically measured the bike (54" high with Cal Sci medium windshield and 29" wide peak) and then found some standard value used online (.84) which comes out to the 9.135
Weight = 950 pounds (being kind here)
Known Engine HP = 160
Approximate (target) Wheel HP = 160*.85 = 136 wheel HP.
To hit that 136HP value we have to be at a Cd of .49 which I think is an unrealistically slippery number for a motorcycle/rider combo but lets play the game.
None of that has to be anything but within the margin of error because what we care about is the relative increase in HP to hit 170.
If 155 is a reasonable number, then to hit 170 MPH we need approximately 180HP at the wheel (204 at the crank) or an increase of approximately 28% over stock. To go 15MPH faster, we need almost 30% more horsepower.