"Ideal" shifting points vary widely car-to-car, and depend most heavily on what your driving habits are at the time (e.g., driving for economy or performance?). Driving to the nearby grocery store and back, I may shift from 2nd to 3rd at 30-40MPH in my car, whereas when I'm in a rush to get to school, I enter the freeway and want more speed
now, I may wait until I hit between 50-60MPH to make the shift. Of course, driving the car around town, I never find a need to take the car anywhere near the red-line so I play it conservative and save on fuel and a bit on long-term wear-and-tear.
Drive in "stick mode" enough, and you might just be able to shift solely "by ear" by recognizing how the engine sounds at certain RPMs and responding accordingly...
Keep in mind that when you down-shift as you said, your RPMs will likely jump 1000-1500 or more, so be very cautious with red-lining here. Some will tell you this is bad for the engine in the long run when simple use of the brakes will do, and others will say it really doesn't cause any sort of significant harm & can save your brakes just a bit. It's up to you, although I've read a few threads before which have touched on this subject.
I'm very tired, and I hope some of this made sense. That'd be a miracle as I'm only slightly coherent right now... but that's another story. At the very least, you get a bump from me.
EDIT: Yeah, what they said, too ^^^
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