Just drive it as it is, auto. then you'll get the feel for when the car naturally shifts. it depends how you're driving it. During normal driving and speed to the supermarket under the speed limit, it usually shifts at about 3k rpm. if you're in first and at 5000 rpm, thats high yes, unless you want to race it, dont know why with an auto, but oh well its your car. it sounds like its going to blow 'cause its getting louder and you're climbing up the powerband. you can redline it at a little before 7k rpm. if you want to do a run that is, though i dont recommend it, like the others said, might not be good for your tranny.
i have an auto too, and have tried out this little feature one time you're speaking of, but i only shift from 3rd to 4rth usually because if you leave it in 3rd, the car will shift automatically up until 3rd gear, then you have to shift it to fourth (semi-auto). Unless you leave it in 4rth all the time then it's full automatic. Yet I find that it shifts more economically, not for performance. It shifts early for you, conserves gas, and less strain on the power, since a stock factory b18b motor and ecu aren't tuned for performance from the factory but for economy. Anyway i usually leave it in third, 'cause for me I feel it shifts better, not too early, feel a little more power and i get too shift the last gear, and i do so just judging naturally after driving for years and also driving stick, by 2nd nature. i just judge depending on my speed and looking at the tachometer too. When in fourth though, this is when the "semi-auto" feature comes in handy, during the situation when some moron decides to stop short on the highway going above 60 in front of you for example, reducing engine speed slows the car down considerably along with braking. I dont recommend slowing down by shifting only, eventhough it can be done, more so with stick. But you would have to learn more advanced shifting techniques such as heel-toe revmatching to down shift, then you can slow down using the engine speed without braking, but for advanced drivers with a stick not auto .But in sticky situations, I have and it has saved me from touching bumpers. to just pull back on that shifter from 4rth to 3rd while braking, gives you alot more control, without the need of a clutch, which I think is pretty cool. Other then that, i dont shift from 1st to third. your tranny isn't meant for it. You will do damage. You can have fun trying it out once if you want. but I would just shift early as the car does, around 3. And that's it, drive auto after that, dont keep playing with it. Leave it in third, and shift around 3000rpm when going to 4rth or just leave it in 4rth. its an auto. im no expert, but thats my $00.02