I have a cuore automatic on CNG, the car drive is ok on cng, but when you turn on the A/C the car response gets really poor, but after you hit 60 Kmph you wont feel any difference wheather if the a/c is on or not.
I got CNG Installed for 24,500 and 40L cylinder, and it gives me an average of 140 km per cylinder which is as far as i think is good.