eerrr....my platz is doing 190 kms within Cantt here in quetta where its all hikes and slopes, pathetic gas quality in quetta. on long route, it constantly gives me 270 plus on GT road (235 on motorway at 120km/hr)....and once (i repeat just once), it did 335 in only cylinder with 3 adult and a child on board (went from pindi to mian jee hotel in lala musa, back to pindi, then to islamabad, and on the way back to pindi it finished)
so yes these types of mileages are very much possible on low RPMs in 5th gear
well done