Also depends on the engine. V6 and above are 2500rpm at 100km/h usually. 4Cylinders hit 3000 to 3500.
4 cylinder does not go that high in 5th. unless its a gsr trans or somethin. closer to 2-2.5. but then again its been a while since i stuck to 100 km/h.
- physical size of your engine
- # of cylinders
- # of gears in your tranny
- gear ratio
Ive had 2 V6's both with 4spd auto tranny's but they were both revving at different RPM's going the same speed
My pontiac bonneville sse had a 3.8L v6 with 4spd auto and at 120 km/h it was at 2200 RPM
now my camry xle v6 has a 3.0l v6 also with a 4spd auto but at 120 km/h it's at 2800 RPM
no two cars are exactly alike, so you can't generalize in this topic.
generally as your engine size, # of cylinders and # of gears increase, your RPM is going to be lower.