It seems like after 100-200 pages of Gravity's Rainbow one of two things can happen:

1. The reader can't figure out what the hell is going on anymore or who anybody is. They give up and stop reading.

2. The reader can't figure out what the hell is going on anymore or who anybody is. They stop trying to make sense of the book and just read the words.

"Sure this guy has a toilet stuck to his foot now, and can prevent bombs from landing on him by magic or something. That's great, oh I think somewhere in that sentence it became 20 years earlier in a different part of town and there are two entirely different characters I don't know talking about something else. That's neat."

I think Gravity's Rainbow is significantly harder than Infinite Jest

I thought Gravity's Rainbow got more confusing as time went on, if you just flow through it yeah its not too bad. But to fully understand the 100s of characters disappearing, reappearing with new names, etc. I definitely found myself consulting notes in the later pages to remember what role someone had played 400 pages earlier. The earlier chapters you can just absorb with no thought for how it contributes to the whole, by the end it is a lot of threads to try and keep in order.

The problem I have with Infinite Jest (I have a paperback edition; USD/my currency is expensive and I'm not made of money) is that the tome is too big for its binding and will seemingly fall apart at any time; and too heavy to hold in your hands in a reading chair (as opposed to propped on a table).

Your advice is spot on. For me it was 100 pages. It was decades ago, but I still remember being puzzled, feeling like I didn’t know what was happening, but being pulled along by the unique quality of the prose. 100 pages in, the lightbulb went on. It’s as if the book teaches you how to read it.

I'm not convinced you can compare Ulysses to Gravity Rainbow and Infinite Jest. Ulysses is not a postmodern book. Apart from their length, there are few things bringing these books together.

Gravity Rainbow has Pynchon's inimitable prose, constant segue between language register and mingling between the trivial and the profound. Infinite Jest is rambling and convoluted but it is extremely funny from the get go. Both can be a joy to read even if you don't finish them.

Ulysses on the other hand asks more from its readers. You can pretty much ignore the references in Gravity's Rainbow and still get (or not get) the point. Meanwhile, Ulysses is full of oblique metaphors and layered references which make it impossible to understand without knowledge of the referenced material.