Have a look on:
www.performancecentre.co.uk
www.motorsportworld.co.uk
www.kam-racing.com will do you a SuperSprint race pipe which is a straight pipe from the manifold to the back box and replaces not only the centre siliencer and the the Cat all for under £80 I think.
Soulless has one with a Piper 3' outwardly rolled back box and it sounds great, ask him
If your thinking about a decat Id strongly think about the SuperSprint race pipe but if you do alot of long motorway runs it might not be ideal because of the extra noise but again alot would depend on the back box itself ie shape, size and brand.