Speed is good but you're never going to be anywhere near movie speed anyway. So what we're discussing is the difference in slo-mo factor. If a movie fights takes 1 minute, then resolving it in 15 minutes versus 45 minutes is (imho) not that important for the cinematic factor. That said, I like to seeing players take decisions under time pressure.
I would disagree strongly with this. Obviously a table top RPG isn't as fast as a film, and I have no issue with emulating movie action over longer time to emphasize certain elements. But there is a very big difference between 15 minutes combat and 45 minute combat. And I just find personally, that the 15 minute combat usually means I am visualizing something much closer to a film than a 45 minute combat. This is particularly true if the combat is theater of the mind. Once the miniatures come out, then I really begin to lose the cinematic feel. Again, I am not saying this is 100% all the time. One of my own games leans on longer combat, and is meant to be cinematic, but it was a design choice because we were focusing on emulating a particular aspect of cinematic combat (so I didn't mind if it took a bit longer to resolve). But just on average, I think there is a loss of the cinematic vibe the longer the combat goes on for (especially if it is taking people time to pick an action, and if rules have to be looked up frequently).