She also asked "Why M35X doesn't need to shift gear down?" I said "at that speed M35X engine rpm should be around 3500. It is always in sport(battle) state and doesn't need any down gear"
I also found GSF received similar MPG as my old G35S...

PS: after 2009 many G/M/Q receive new 7 speed auto which improve MPG on highway. (but in city MPG is still about the same)