Isn't it just some sort of training? Most people I know start of slow, but once they've gotten used to it, they get quicker and quicker in reading the subs. People complaining about subs that are too fast usually only lack the experience, they are not (yet) used to it.
I usually just look at the sentence and "see" them as a whole. I don't really "read" it like I do with normal text, if that makes any sense to you guys.
When I watch a normal television show, I see how huge the influence is, that subtitles made on me: My eyes usually twitch to the bottom of the screen for a split second several times, before I realise "oh, no subtitles there...right, I actually do understand the language, that's why".
In all the years, there have been only very few occasions, where suibtltes have been so fast, that I had to stop and rewatch something. But in 90% of the cases it have been scenes with a lot of dialouge AND some annotations on the top of the screen, like an explanation of a joke, term etc.
The problem with timing English subs from Japanese has to do with the actual languages. Eg. An opinion which takes 5 seconds to communicate in English can take 1 second to communicate in Japanese.
Maybe it's a consoling fact, that English is quite a "short" language. Books translated from English into German usually are 30-40% longer after the translation. ;) This is the main reason, why I always prefer English subtitles over German ones...they are simply much shorter.