Why a 4spd not 5spd AT

[eTiMaGo]

Originally Posted by watersoilair

Wouldn't the 4 speed transmission get poorer fuel economy over speeds of 90km/hr? I was told that 5th gear is like an overdrive of sorts. For instance.

If I were to drive 90km/hr in 4th gear it would definitely be at 3000 no questions asked. If I were driving in 5th gear at 90km/hr it is ~2700rpm. The split seems to happen ~85km/hr when both 4th and 5th gear runs at 2500rpm.
The tach gradually moves up to 3000rpm and above as I drive faster. ~3300rpm at 120km/hr and ~3500 at 140km/hr.

Then again, on the 5 speed manual, we run at about 3000RPM at 100km/h too... I think the gear ratios for AT4 and MT5 are pretty much identical?