I know this was a horse, not a dog, but I feel that it is related.

You are the one that knows your dog the best! I bought my horse from a lesson barn where she had been for a year, and almost immediately moved her away from there. After 7 months I told them that she was dead - euthed. I got HELL for that! I was a murderer, a killer, a beast, I made things easy for myself so I could get a new horse, and so on. But hey, THEY had not seen her every day, seen her struggle, seen her hurt, had they? They had not talked to the vet. Or seen her pain when she was walking around, seen her being stiff, stumbling etc. True, it was not really her time to go, she could have lived on with only moderate pain as it were, but she had athritis in her hocks and front knees in addition to her sore front feet (Navicular) and it could go downwards so fast. I thought about it a lot, and decided that I would rather euth a month early than one minute late. So I planned it carefully, got a good vet to come out, planned the time carefully, and when the vet came she clearly saw that it was time for my girl. I cried, but it was also very good, because I knew I had done right on her, and kept her out of suffering.
Now I know how I want it to be, I want it to be like with Basse. I know that the pain of knowing I waited too long will be greater than the loss (Which is inevitable anyways). I will much rather say goodbye to a reasonably healthy and happy animal than to an ailing animal in great pain.