And would I see a worth while increase in performance ?? And also any tips or advice any one can give to help ?....

If more noise = better performance then it will be an improvement but in the real world you will find very little (if any) difference. Years ago standard exhausts were very restrictive, that is not really the case today. The main area where there are real improvements can be found are in the manifold, the cast ones are fitted simply because they are cheap and easy to fit. Tubular ones are generally where real improvements can be had, at a price.

You must tell your insurers since they class such changes as a modification.

Whats the score on getting a standard non performance stainless system made up when the mild steel version rots away, whilst a sensible alternative for some people is it still an insurance problem?

Reagrding our OP's situation, i too doubt there will be any worthwhile power gains unless you're losing a secondary CAT or something, and whilst i can fully understand someone with a V5/6/8 etc desiring a bit more enjoyment of the sound of their engine, a straight 4 is, IMO, just about the most horrible sounding engine ever made and the exhaust should be as unobtrusive as possible....unless this Vexer happens to be a V6 or VXR of course..;)

Edited by gordonbennet on 18/02/2014 at 14:56

V6's can sound pretty good too, 70's Grannies and Capris sounded lush enough to me.

For a proper engine sound fix listen to a few Deltic Trains with their lovely Napier two stroke supercharged Diesels on Youtube, heaven.

With close coupled cat(s) most of the back pressure is in the 'hot' section of the exhaust rather than the silencing. If you drive the car hard mild steel is perfectly sufficient for corrosion protection.