FYI - RPi4 UEFI firmware version 1.4 was released today with an option to disable the 3GB limit at runtime:https://github.com/pftf/RPi4/releases/tag/v1.4
Nice! It took me a while to figure out where to make the change - I'm still getting used to the idea of boot-time options on a Pi - but that's great!
However, even a brand new kernel stops right before the "cpu0: PMU interrupting on irq 48" line when booting.
Moving back to 1.3 boots all the way. Thanks, John