Is this the time for one sample because this is not the sampling rate you will achieve in practice since there are other things like doing stuff with your sampled signal and that will slow down the overall sample rate. So it is a bit of a non question.
However the last time I tested things I got:-
Due 1000 readings in 3mS in IDE 1.5.7
Due 1000 readings in 40mS in IDE 1.5.3
and The Mega I take to be 10KHz although it is slightly under.
Get the full list here:-
http://forum.arduino.cc/index.php?topic=326944.0