Zx25R owner here. if you are going to use it as a daily driver at a distance of 140km++ then you are better off with a bike that has a upright riding position. i use mine as a daily driver at distance of 23km++ one way and all i can say is that riding to and from work is fun. I am going to test it for long distance run this Dec 18 to Perlis and will update here later. Oh yeah almost forgot to mention. Fuel Economy is based on how much you speed on the bike.

Actually it is not the back that is the issue on sports bikes. I own a Benelli Leoncino 250 and from a Naked to a sports bike riding position of course different. On the naked my lower back hurts but on the ZX25R my shoulders and wrist hurt back is totally fine.