Will likely take 1-2 years of consistent work before pup is trained enough to be left alone with livestock.
This is an excellent resource for learning to train dogs for livestock:
http://www.homesteadingtoday.com/guard-animals/
Breed can have little to do with a dogs behavior,
has a lot to do with environment and how they were handled/trained during their brains formative period(8-16 weeks),
and how they are handled/trained from there on out.
I agree it has more to do with the particular dog and especially that dogs owner/trainer than a particular breed....there are no bad dogs, just bad dog owners/trainers.
I'm sure there may be LGD breeds that tens to be more aggressive, but I don't know what they are. Got to...
Donkeys and llamas, and alpacas can also kill the animals they're meant to protect.
No guard animal is foolproof, you need the right animal - which can be luck of the draw, and with dogs at least you need the right human to train them properly.
Any dog will need some pretty serious training, so if you're not up to doing that you could just be introducing another problem. Here's a forum with some good info on LGD's http://www.homesteadingtoday.com/guard-animals/