ATC is expecting your arrival to be 300kts. Routine arrivals of 280kts will make your's and the controllers job more difficult. The NG does a nice arrival programmed at 300 kts. If you're not quite familiar with the VNAV DES PAGE 3R & 4R information, give it a try. Start your descent when the V/B=2.7 degrees and match your V/S with that in 4R. YOu'll love. Just remember to changeover from Mach to IAS at 300 kts or you'll get the clacker.