Actually, in La Liga, Rea Sociedad is also not a small club and has sometimes given good surprises. It's just a matter of how Real Madrid can optimize its performance again or not. But usually, Real Madrid will be superior to this club. If you look at Head 2 Head, Real Madrid clearly won more. Meanwhile, on the other hand, Atletico vs Valencia, I believe Atletico Madrid should not experience high obstacles. Valencia didn't start the season very well. They are still inconsistent and sometimes cannot optimize their chances. Here, Atletico Madrid might still be able to gain more advantages than Valencia.
Meanwhile at UC, you could say that Lazio is tougher than Berlin. However, no one can guarantee that because sometimes German clubs can also provide quite strong surprises in the Champions League. But of course, which club can handle more, the results will be more optimal.
Real Sociedad is one of the promising clubs with having reputation for staying at the top of the league table and their performance is also mostly we organized which helps them for keeping in-touch with top ranked clubs this match could be not easy for the Real Madrid even they are playing at home and have enough chances with their performance is also at the best after having all 12 points form first three games.
Atlético Madrid is having impressive start with Valencia is having poor start even first two wins were good but now things coming on normal with 2 defeats are surely not good for them with now having fifth round game against Atlético Madrid which is currently one of the best team for better results and staying at the top ranks for few more weeks.