kindly gets the facts correct.
engine capacity donest define gear ratio. gear ratios are independent set inside gear box.
if yr driving slow in final drive with low rpm, you simply loose engine performance, fuel used wont be so much different than driving at same speed with engine running at effective speed. example. 3rd or 4rth gear.
aproaching uphill you have to press gas padel more in 6th gear, better is to shift down to 4rth or 3rd and get better engine performance, otherwise you just loose your speed.
engines running at higher rpm in final drive wont be that effected approaching uphill. because engines are in effective performance speed.
in pk speed is limited to 120 so too many gears dont matter that much, in germany if your going at 200km plus, 6th gear will be effective in long run .
secondly the 5rth is not a final drive so it will give you more acceleration compared to 5th of 5 speed gearbox.
Im coating from a test done with toyota trueno 1999, blacktop20v 6 speed and 5 speed cars
speed limit is 120km on motorway , not 60km. you will cause someone to hit you from back, people expect all to be going at 120.km