Í wonder if visualizing what you read slows people down.

Not really, I can read very fast too and also visualize it at the same time, like full blown movie. I think it’s more indicative of information processing abilities in general: I can generally keep up watching lectures at 3x speed and notice things on screen almost instantly too.

I’m super efficient at filtering information too: I’ll look at a paragraph in some documentation and immediately see “If you’re in X special case, then…” at the 5th sentence in the middle of the paragraph when skimming through documentation. Or of course skipping details I don’t care about.