U seriously need to call me. I have been done with exactly same thugging. and have my article a page or two ago on this very forum on this very issue. Yes the average drops, noise increases.
and there are solutions to it. and they work fine.
google for images of "sparkplug defoulers used as O2 sensor extender" and "O2 sensor wiring 1uF capacitor 1Mohm resistor"
incase i am unable to motivate you, use torque with ODB2, and find that you have dropped your average from 21+ to 12.5or13km/l just by removing cat.
cat is available at saddar ahata and khooh. around 7 to 10k pkr. ...... i ve done the extender solution, it fools the ECU to show the cat as present but does not bring fuel average back. hv personally tested, n hv done wiring stuff just couple of days back, if result is not satisfactory, heck i ll be going to rumbles for finding a suitable cat.
cats.... ah the cats. how much we dont know their usefulness.
b/t/w nowadays working on direct port control. i.e controlling via laptop, and programming the ECU to comm with Wifi etc. aim is that Ek should send periodically check all signals everytime, driving or not, even when we r away. and report it live to an interface, this interface reports data to a web interface. maintains logging. and hence we can get a complete record of what n where the WTF happened. plus security, whenever data logging stops, or any of the sensors go really wild, it should email, sms and call us to let us know that EK is not there, or behaving like a badbaby. but thats boring i know. apologies for disturbing.