what i think a lot of people have said is that 'around town' or in areas of constant changing road conditions (this means traffic lights, hills, dips, braking and accelerating often which generally happens in 60km/h zones) if you have o/d ON, then yes the car will be sitting at 1600rpm. BUT as soon as you accelerate or hit an incline of any sort you will find that the car kicks down to 3rd and once you get up the hill it goes back into o/d. factor in this sort of event happenning 5 times in the space of 5 km and you will have changed gears 10 times. plus driving like this allows the car to run under load in o/d which cannot seem good to the greabox from a logic point of view.
so if we decide to turn o/d OFF, then in the same instance as above there is ZERO gear changes with greabox wear reduced significantly.
so, what is the best thing to do?
some will say drive with o/d on, some with o/d off.
and obviously the correct answer is that its up to you.
I say driving with o/d OFF will cause the trannie to run a tiny bit hotter and also cause worse fuel economy although both will probably be an insignificant amount. Driving with o/d ON is really not for 'around town' conditions, thus why its a button-feature and not a automatic fourth gear.
Just assess the road conditions ahead of you. if there's a flat road for a long stretch then put o/d ON even if you're doing 60km/h. if you're driving in the city/inner suburbs doing 60km/h then leave it OFF to save grearbox wear. in all instances if your speed exceeds 80km/h then i can't justify having the car revving above 3000rpm for an extended period when there's another gear there so always put o/d ON at high speeds.
my 2c anyway
cheers,
Warren.