in your car is 2003-04 model then there are two CAT converters and in the older models(99-02) there is only 1 cat.in our cars one cat is placed inside header and the second one is in the exhaust pipe so there being two CATS there is more resistive force in the exhaust flow and if it gets choked then car consumes more fuel and not performs up to the level so first remove the first cat by breaking it and not welding anything out there if its in good shape then leave the second one cause there must be no blockage in the second one if the first one is clean the same case was with me so i left the second one as it was.
the place which other members also refer and i got my cat removed is at gizri the name is i think bismillah silencer works or something like that and its placed next to Zafcom(the famous tyres and rims sellers)
didnt measured the average after cat removal as i have done it recently,and the sound comes now is not bad!