2m+ travel lengths with a ballscrew, using linear rail to support the ballnut

[Desertboy]

You're in Cuckoo land if think direct drive 400w servos are going to spin 2.5mtr long 25mm or 32mm ball screws at high speeds.

On the rail idea why spend £250 plus on rail system which will be a pain to implement when there are much easier ways to avoid or deal with the whip.
The best way to deal with the whip is not to have it in the first place. So choose the method and size the components correctly and you won't have the whip.

Would be better spending £250 on building rotating nut system and take whip out the equation.!

What size do I need? 1.2kw?

Rotating nut is considered as well ;) It's just I only vaguely understand how to make it work.