I would look at pure:dyne, it has realtime kernel and freebob.
It is designed for live performance, uses lightweight window 
managers (evilwm, xfce, dwm, ratpoison), and boots fairly 
quickly.  You can create your own modules from rpms, debs or
source.

     https://devel.goto10.org/puredyne

The pure:dyne community is dedicated to live performance and 
I am sure they would help you configure your system for your 
requirements.

What is the single application that you want to run?

danni said:
> Very Specific Requirements.....
> 
> Must boot quickly -- Ability to turn off hardware 
> autodetection easily highly desirable.
>
> Must be fairly straight forwards to customise X to run a 
> single app rather than a window manager.
> Prefer a realtime kernel out of the box. Must have working 
> firewire by default.
> Must be relatively straight forwards to build software on 
> or for and package it.
> 
> Basically I am looking to set up a single app box to be 
> used in live performance. If something goes wrong I want to 
> be able to hit the reset button and have a working system 
> again in the minimum with no human interaction other than 
> the grub loading screen.
> 
> Any suggestions
>	Danni