I agree thats the proper way especially when doing a race car, but most people seem to run 3.23-3.55 gears no matter what, so If that's all the gear your gonna run with, pick parts that's gonna give you more under 4000 rpm since that's where you engine gonna spend most of its time. But also when selecting parts try extend the powerband to the point if went any more you would start give up bottom end for top end, because there no point pick a cam that's gonna give you 30hp extra at 6000 rpm and sacrifice 30lb-ft down low if car rarely see's 6000 and if you need more power then that, go with a bigger engine.
