But this 4stroke is 100lbs heavier with similar power to an 850 at 6500ft.
Not Quite. The claimed weight difference between the 2 Stroke and 4 Stroke versions of the Renegade is 41lbs and your 850 is at about 130 HP at 6500 feet. See below.
HP Loss = (elevation x 0.03 x horsepower @ sea level)/1000
32.175 = (6500 x .03 x 165(claimed)) / 1000
132.8 HP @ 6500 FT