How do you know the choice's right?

Some of you may know that I'm looking for a second dog. It's an really exciting time, I can barely wait to find the perfect dog for my little family. I've come to the choice of getting a sheltie bitch puppy. I feel like I've an pretty high standard for the puppy. First off, most of the bloodline should be tested for PRA and HD. Could accept some exceptions if the tests are clear for the rest of the line. I would like to be able to use her in shows and obedience, maybe another sort of sport if she likes it more. I don't want her to be related to Beethoven. Mentality are very important for me, so it's important that the dam and sire are stable dogs that aren't nervous and that they can handle new situations without much stress. I could accept barking and vocal use, as long as it isn't hysterical barking on everything that moves.
I plan on using her in breeding, that's why I'm keeping such high standard. Of course, things can go wrong, so she won't necessary be suitable for breeding purposes. But I'll try to get a good starting point as possible.
So the last months I've been studying pedigrees, health statuses, show results... All possible things there's to find about the dogs. I've found some promising dams, and also some that gave me goosebumps (not in a good way.). How do you really know you've found the right combination? It can look good on paper, but you never know. I guess it's just to follow the gut feeling if everything else seems to be perfect. No one are psychic, so just time will tell what the result would be. I still got plenty of time, so there's no rush on the decision. But it's nerve wracking this waiting and researching period.

Beethoven 8 weeks old.