I agree about the relative strength of hi-starts. Mine is really intended for larger planes so I just don't pull it back as far.

My friends hi-start, the dynaflite HD launches his spirit just as high as my hi-start sends mine, but his goes up more gently. When I pull his back it is not nearly as strong a pull even though I have walked back much further.

So, which hi-start? Make sure it is strong enough for your plane. I would say that for a 2 meter minimum would be 1/4" OD and would strongly suggest 5/16 so that it has plenty of power for still air days.

One advantage of the stronger hi-starts is that you don't have to pull them back as far so you don't need as much room.