Shakespeare is a definite barrier.

I normally don't use a "voice" in my head when reading, but doing so is invaluable when reading Shakspeare. If I can't "hear" what I'm reading, it's much harder to parse.

I can get to 1300, though it’s harder there and there were a couple words that I just couldn’t figure out.

For me 1200 is off a cliff, just like the author describes. I can get a few words here or there but comprehension is just gone.