Ive tracked mileage on my longer rides on the Nytro. I get a range between 5.8km to 6.8km per litre - depending on snow conditions, temperature and how much you ride wot. The usual results i get in most snow conditions/riding were about 6.3km per litre.
So on a 28l tank using a safe conservative range of 6km per litre, expect to get at least 168km
I owned a vector with the same engine and it would produce very similar mileage, just slightly less due to its weight.
So, on a viper with a 40 litre tank you should be able to easy get 240-260km as the nytro and viper weigh about the same.
Hope this helps.
MS