mpg on a 250 x

hi
have not had our bike long, how many miles will it run till the reserve comes on ?
and then how far can you expect to go after that point ?
for one reasor or another we have not yet got to get a mpg average to see what it will do.
the bike is ridden easy on the road, its my wife's bike and its not getting abuse except when
i ride it when she isn't looking .....................lol !
now if they just made it in the 300-350 range from the factory that would get my attention real quick, its a fun bike but for me i would need just a little bit more performance .
but by no way i'm i knocking the 250 concept !
its a really neat bike !
thanks