why does it look horrible?
maybe you haven't rendered it?
maybe you should un-tick the "frame blending" option.
a 300% speed up without frame blending should be exactly the same as cutting out 2 frames in every 3.
another thing to keep an eye on is that you might ask for a 300% speed change,
but depending on the number of frames available, you might not get an exact 300%
to get an exact 300, it helps if the number of frames in the source clip is evenly divided by 3 (or is that 300?)
control or right click in the timecode and duration fields in the timeline and/or canvas, and choose "frames" to see the duration in frames.
hope that helps,
nick