if it was showing 165ish you were probably somewhere around 150.. .. no more than 155 I'd say. The speedo is pretty off at those speeds... Mine was showing basically pegged, but GPS was showing 160.. not in 4th.. I'm just showing how far off your speedo can be at high speed.
Not to likely if you are running stock gears (but possible). Top GPS in 4th gear should only be 162.9 151.5 = 5th=184mph and 200mph in 6th. That is perfect conditions no wind etc. Average in 6th for stock is 194mph with an average rider. Even running 18/40 which would get you to a 3 percent variable. The average is bettween 6-7.5 percent off. You could also change these firues by using a 78 inch tire (which is 1.5 inches bigger then stock. i have not seen anyone do this with a stock bike because of HP needed to turn the tire). You have to be careful at those speed becuase you can get bounce etc for true readings. to really check how close you are borrow a GPS unit and compare at 65mph and at 100mhp and 130mph check the variable, i think you will be surprised.