You can combine the two methods. So to get your desired 1000% you could use a 250% envelope combined with a 4X playback rate.

If you need even more, you can use a script. I don't know if there is a free one but the excellent Peachrock Veggie Toolkit contains one called TimeBandit which will handle this.

Alternatively, if you don't want to spemd any money, you could use a frame decimation approach. Render out the clip as an image sequence, delete every frame except those you need to keep, renumber the remaining frames and re-import the new image sequence. E.g. for your example of 1000% (=10x) you would delete all but every tenth frame, i.e. keep frame 1, delete frames 2-10, keep frame 11, delete frames 12-20, keep frame 21, delete frames 22-30, etc.

Mark