I have Santro GV 2008 Recently started using CNG. Cylinder is fueled with 8.8KG and car traveled 148 km with a speed of 130km/Hour on M4 That too with continuous use of AC . In my opinion most important thing is how you get the adjustments done.
I tuned it for CNG from an OGRA certified CNG specialist now my car is working better on Gas than Patrol.