If you run the cable up along the roofline, which is how I run mine, then the 6 meter should be plenty. If you decide to run it along the floor, you may need the 8 meter.
If your sure you do not want parking mode, then just get the Viofo basic 2-wire hardwire kit, which will turn the camera on/off with the car. You can use the 12V cigarette port on your car as well if you want, as long as the port turns on/off with the car.