Well, the simple logic I go by (even tho I don't really sit around making setups but I'm learning

) is to adjust the final drive (basically the general top speed of the car) to make it so that the car reaches maximum revs down the longest straight in top gear on the course and then I just adjust the gear ratios in between for acceleration or traction. I learned that bit from the lovely GPAEDIA which comes with Grand Prix 4 which has some vids on making setups. So, I got that from a guy called Mark Hemsworth whom I think was an engineer in the Arrows F1 team so he does have credibility.
As for the whole peak torque/peak power thing, from what I read from a book called "Ayrton Senna's Principles of Race Driving", he stated that the best time to shift is a bit after the peak power so that you maximise the speed you get from that gear and when you shift gear, the next gear is at the peak power of the engine, thus giving you much better acceleration. Thats what I've read and seen, don't blame me if they're wrong

but I do think they know what they're talking about and it is logical.