When you speed read you pick up phrases and even whole sentences at once.
In a language that doesn't use capital letters so much, they stand out and whilst speed reading you do need to slow down a bit and figure out what's weird with the sentence being read. You can no longer just directly pick it up, you have to read it one notch slower and build it. This can be quite noticeable when speed reading. It happens with large words too. As you get used to certain capitalized words (names in a book, common large words, things like Internet) this speed bump decreases, but it's still there for people.
In a language that doesn't use capital letters so much, they stand out and whilst speed reading you do need to slow down a bit and figure out what's weird with the sentence being read. You can no longer just directly pick it up, you have to read it one notch slower and build it. This can be quite noticeable when speed reading. It happens with large words too. As you get used to certain capitalized words (names in a book, common large words, things like Internet) this speed bump decreases, but it's still there for people.