Decat Exhaust pipe good or bad idea?

Ive been reading alot about decating my exhaust to allow the engine to run limit free. A decat pipe is about _Ǭ£80 so does anyone know roughly what sort of power gains i can expect from this? does it make that much of a difference? also what do others do when it comes to MOT time is it just a matter of swapping the decat pipe for the cat before i go for the MOT?

"well ive been told numerous times a decat will make a big difference. and considering my was 169bhp as standard then with just a induction kit and full stainless system and a ecu chip its now running over 200 i would say yes a decat does make a big differnce. Also you tend to get a much more throatyer roar from the exhaust also with a decat pipe. Ive never had a car where i have fit a decat pipe so sadly i cant comment on what the differnce is like as ive only ever had a car with a cat back system and the 200 well thats a complete de-cat system. but id say fish around i payed 60quid for my decat pipe for the bravo (but never got round to fitting it) but if i was you id give it a go no harm in trying is there. as for the MOT if your car is pre 90s then you can get away with not having a cat. Otherwise its a bolt on before MOT time im afraid "

"You never know it may pass the emmissions test with the decat on. My R is a 91 so no need for me! The standard CAT will defo be restricting flow although what actual gains you'll see will be minimal. To see any great gains your going to need to put a few parts on together. You'd be better off saving the _Ǭ£60 to one side to put towards a car witha Turbo - Much more fun to mod! "

"a cat is a big restriction but what gains youll see really depends on what sort of power your starting with. generally the more you start with the bigger the gain will be. as is always the case though every little helps. John"