with enough math, you can be pumping the same number of "notes" per second even if the tempo of the song is 20bpm.
Yup, it's like the Freespace Theme, it never ever changes speed, only difference between the beginning and the end is that at the start they are playing in Crotchets, Minims and Semibrieves, (1,2 and 4 beats) and by the final combat scene it has been stepped up to Semi and Demi Quavers (1/2 - 1/4 Beat) which means the notes are coming 2-4 times as quickly.
For it to be a true 1000bpm, you would have to be able to play Semi and Demi quavers between each beat, thus making something between 4-8000 notes per minute, which is impossible, however if you do it at 250bpm, and play using DemiQuavers, it becomes a lot more likely.
Look at it this way, even Cubase only allows an upper limit of about 300bpm, because it can't process the Audio any faster than that.