ANSA,
I know a Watch manager there.They have days of 700+ and mid 50's an hour.
I have done that single runway job at those traffic levels,and it ain't easy.But you have to get your ass in gear sometimes,otherwise they just sit there wasting fuel.As Seaman Staynes says everyone has to play the game.The operators at Gatwick(most of them) use high speed exits,at high speed.
PS.The CAA's figures for EGKK are 261,292 for 2005.That's a wee bit more than you stated.Using your method that's about 715 a day.So on busy days it's got to be 750+.I'll put my handbag down now.