Yea its best to play it by ear. However I shift at 3k at normal driving because its easier on the clutch. If I get up to speed and Im in 3rd at 2600 Ill shift to 4th to save gas. Ill only put it in 5th if Im going 40 or faster or 35 on a flatter road. Cobalts dont really like to be short shifted since the gears are pretty long.
well keep this in mind... if your car is bogged down due to low rpm, your car will get shit for gas mileage and it puts more stress on the engine. if you have your car too high on rpms, you do shit for gas mileage and put more stress on the engine than what is necessary. find that happy median... 1500-2000 is a pretty safe zone where you're not bogged down and you're not too high either.
Personally, ear's more important than tachometer. After all, it would be better put your vision at somewhere else when you're shifting. Besides I think the best RPM for shifting among different vehicles are apparently not the same~~~
i shift by listening to my car, not by looking at the tach. i was just giving a better estimate... it's not like you can tell someone over the internet "hey when the car sounds like this 'insert sound', SHIFT!"