This thread certainly has fired up in the months since I originally posted! It probably would be right to post an update on Douglas. He got his "procedure" last Friday, at about 7.5 months old.
Deborah is right--I originally posted to try to garner a variety of opinions and perspectives on the matter.
We are a single-dog family, with a cat and a dwarf rabbit, so ever since he had his initial shots we have been taking Douglas to the nearby dog park to play. He has made many friends there with whom he loves to wrestle and spend time. In short, the dog park is an inseparable part of his life now.
Since around 6 months old, Douglas was starting to exhibit some tell-tale traits that he was going through pupuberty. The resource guarding got worse, in spite of positive counter-conditioning, and just this last month he's been constantly searching for spots where other dogs have marked--drooling when he smells them. He didn't start lifting his leg, but he was starting to mark by squatting. Furthermore, "come" (90% success rate before), was now only working about half the time at the park. That was the straw that broke the camel's back for us. Although on one hand, there are a handful of scientific studies that suggest waiting until full maturity to neuter giant breeds has positive impacts on their health, we could not bear to keep Douglas from the dog park and his friends for 2 whole years. It would most definitely have impacted his emotional/physical well being.
We made this decision for the safety of other dogs at the dog park, but most of all for Douglas' well being and happiness. It is what works for our family at this time.
P.S. His recovery has been going great! No vomiting or diarrhea, and he got his appetite back the night we brought him back. The surgical site has been healing nicely as well, I think he will be okay to go to the park this Friday or Saturday
EDIT: I forgot to thank everyone for their insight! Your opinions and perspectives along with advice from our veterinarian have been instrumental in our careful decision-making process.