I personally think you need at least a good 300k range.
My klr has a 300k to empty range and I start thinking about filling up at 200-230km if I come across a gas station unless I know for a fact that there is another one on my intended route comfortably within my range.
Its not how far you can go on a tank of gas but how far you can go before your concern over where you next need to fill up starts to influence your rides route.
I hate not being able to suddenly decide to go a different route because I'm already 200k into my range and I don't know exactly how many k's the new route is.
more range is gooder unless the petrol weight compromises handling