The studies on spay/neuter aren't as clear cut as some would like to say. The earlier studies did not include enough breeds, did not account for whether dogs were spayed/neutered at 6 months or after maturity, etc. People wanted to generalize those results to all dogs.
However, it does seem to be emerging that waiting to spay/neuter in larger breeds is advantageous in many ways, most specifically in a lot of cancers and definitely in the risk of CCL injuries. The risk of some cancers in females do go up. As always, it's not a black/white issue, as much as many people want it to be.
Personally, I do find that the advantages of waiting to spay outweigh the risks, however, I do think that, in females, spaying is the right choice if you aren't breeding. Pyometra is a real risk, as are mammary tumors. Pyo is, by far, the biggest risk in intact females, and for me, there's no reason to risk that.
For us, the optimal age to spay was about 4 years. It was well past the age of any risk of personality changes. (There are some studies that suggest that spaying *could* cause a change in fear/aggression, but it's far far more likely in a young bitch.). 3-4 years old was old enough to have a set personality, old enough to have protected her joints, and gained any benefits to delayed spaying.
These are my feelings based on extensive consultation with my vet (who is well versed in reproduction, and is a good breeder herself), my sports/rehabilitation vet, my breeders, etc. The science on spaying/neutering
Your mileage may vary.