I am not sure about the capacity myself either, nor do I know how much kms she runs with 500 rupees of CNG. But I do know that in one cylinder (which now gets filled in about 675-700 PKR) it gives me above a 100 kms within city. If I drive keeping the economy in mind, I can pull out a few kms more. On GT, it takes me to Jhelum with some CNG left in the cylinder before getting a refill.
Pick is not an issue at all. I can drag it with a 1.3 VVTi running on Petrol and can pull it above 100 on the second gear. If the CNG is mixed with too much of air, then yes you do face some issues but the RPM adjusts itself automatically after you drive it for some time.
People's "NO" can change into "Yes" if they keep their cars properly tuned. Plus, the car's engine is in perfectly good condition and it started running on CNG after 50K on the ODO. Still gets the Petrol tank filled every week.