Funny you say that about Presage Flower's pacing, because I have the same complaint, only about Lost Butterfly.Fate stay night is easily the worst I've seen of those stories. UBW is, as you say, better in every regard. Zero has probably been my fav so far though Heavens Feel has got off to a great start even if the first act of that film is terribly paced.
It's true that the first movie's opening 30 minutes take their time, but generally I found the movie extremely fun from beginning to end with just about enough action scenes interspersed throughout that I never felt bored
(Herc vs. Saber, Saber vs. Rider, Lancer vs. Assassin, Caster vs. Everyone, Assassin vs. Saber and Rider vs. Assassin).
Meanwhile, in the second movie,
after the Shirou vs. Rider scene, you have a lot of movie where there's not a whole lot going on, apart from character development, but it felt a bit too long for my tastes. I'm not even sure it's a long time, but it felt like it. The only action scenes in the second movie are Shirou vs Rider, the huge action scene after the middle of the movie and then Gilgamesh kebab, if I remember correctly.
Still some of the finest anime movies I've seen in quite some time. If they stick the landing with Spring Song, we'll have ourselves an amazing trilogy