i have a Vxr 2007,
Not factory fitted cng, 55 wala cylinder ha and it always do more then 200 km on highway and once i drove it really economically, it gave 245 km. I am really amazed with my cultus, on the other hand my vti give only 120 km on highway.
I believe if i drive my car from Islamabad M2 at 80-90 it will give 300 km per cylinder, but never tried this.. Will try it whenever got a chance.