Here is a scientific review by Rutgers University of over 50 peer reviewed, published articles on the long term effects of spay/neutering. I think this is what Cowboyflop and Smart_Family are referencing. I would really have a look at it, before making your final decision.
http://www.naiaonline.org/pdfs/LongTermHealthEffectsOfSpayNeuterInDogs.pdf
Anecdotally, in over two decades of keeping giant breeds (GDs, IWHs and now an EM) we have never neutered, and we have kept between two and four intact males in our home with no problems. Our dogs have not turned into Godzilla when they matured. None of our dogs has ever had severe arthritis or osteosarcoma (or other cancers). On the other hand, our adopted IWH, who was neutered (obviously too early), is tall and lanky, with spindly versus strong, dense bones. At six yrs old, he suffers from arthritis in virtually every joint to the point that he has trouble walking up stairs.
@ charger
It is not the case of their becoming underdeveloped, in terms of weight and size. My IWH is over 38" tall and weighs 190 lbs. It is a matter of the insufficiency of their skeletal structure -- and their ability to carry their weight without developing issues. Also, neutering at any age is increasingly linked to osteosarcoma.
