My 2015 P85D-Ludicrous had 253 Rated Range at 100 percent when first delivered May 28, 2015. On May 12, 2017, 2 years and 11600 miles later, the Rated Range at 100 percent was still 253 miles. My current 90% is 228 on the touch screen (227.80 as reported by Remote S), compared to 227 when newly delivered.
Possibly contributing to this low degradation, other than low mileage: The car has not been driven very hard, has rarely been charged to 100 percent, and has seldom been Supercharged. I usually hook it up to the Tesla 80 amp wall charger when parked, so the battery seldom dips below 65-70 percent, although I had one white knuckle trip where it got down to 11 rated miles. My garage is air conditioned, a favorable factor in Houston's hot weather. None of these range numbers are in Range mode.
My experience suggests that 250 Rated Range after 30,000 miles is quite good. I hope you bought the car.