Thanks for your quick and thoughtful reply.  I agree on all counts.  I have since spoken to R.K.Anderson, the "gentle leader" inventor and emeritus behavioral Veterinary Professor (his office is next door to mine). He said that in over 15 years of carefully controlled cross-species studies no one has ever shown a reliable link between testosterone production and any facet of bone or muscle development.  In other words, animals castrated prior to puberty show the same quantity and quality of skeletal-muscular development as intact animals.
He also added that in dogs in particular, innate personality + early socialization + later learning far exceed any impact of testosterone on behavior.  Thus, a steady laid back puppy who is properly reared with reasonable discipline is not going to turn into a monster if left intact "too long", nor will an aggressive or neglected animal have its problems solved by castration.  That said, the intact dog is slightly more prone to roaming, but this behavior will reverse with castration at any age.  Other behaviors may be learned during puberty (e.g. sexual mounting) which will not recede after later castration.
I will add, as a psychologist, that the studies of "genderization" of neural tissue have all shown the primary effect of testosterone on later behavior patterns occurs in utero, not during puberty.  So if you give an XX chromosomal (female) fetus testosterone exposure in utero, she will grow up to behave in "male" ways, but if you neuter the female at birth and give her testosterone later, she will still have a "female" brain and female behavior patterns.  Of course, this work was all done in species such as rats with strong sexual-specificity in behavior patterns.
So the bottom line is that it really doesn't matter that much.  Even the cancer-preventive value is small in males and is not terribly time-sensitive given that neutering occurs at some time in the first 2 years.  The main effect is preventing unwanted pups.  Therein lies the recent impetus toward VERY early neutering (e.g. 8 weeks).  I found that somebody figured out that once a dog goes out the door of the humane society or breeder there were some that would never be brought back for neutering so they wanted to see how safe it was to try to neuter as many as possible prior to placement.
Thanks for your continued support and have a great time in the Southwest!