I am owner of a GTO 125. It's LHR Number and 1989 model, but it's pick is way too good as compared to other brands of 125cc. As far as the mileage is concerned, I fill my bike's tank daily for Rs. 150/- and I use it as a daily drive rfrom Malir Cantonment to M.T Khan Road (two way, back home as well) and then at night I visit my friends in Gulistan-e-Jauhar, but it doesn't bother me with regards to fuel. Also, I bought this bike about one and a half month, but it didn't give me a single piece of work except the clutch wire change, which was upto my discretion. My bike is in normal condition, no any tip tops or so, but it easily gives a smoke to other bikes of its category, although I don't accelerate it much, but some times .
I use Shahrah-e-Faisal for my way to office and back home.
This can give you a fair idea of GTO-125's fuel consumption, maintenance and performance.