All good ycastane. Here in the states, the rear leg is usually cured and sold as ham. I've never had the rear leg (other than ham), so I really can't tell you about a difference in flavor. Looking at the whole shoulder, the picnic has a stronger flavor and less fat marbled through it. Some people cook the whole shoulder for pulled/chopped pork, while others go with the butt, and yet others go with the picnic. Kind of comes down to personal preference. In any case, you cook all parts of the shoulder until it passes the poke test. This is where you stick a probe or toothpick into it and when it goes in with no resistance like a knife through butter, the pork is ready. Generally, this is in the neighborhood of 200 degrees, though it might be 205 or even 210.
This is why I don't cook these cuts by temp, as it can hit 200 and NOT be ready to pull.