Crazy Slow Workflow in Premiere with big Project

I am working on a feature documentary in Premiere (we have like 7TBs of footage) and it has been working so slowly that it is almost impossible to work. Everything is slow, playback, dragging, copy/pasting. I have tried almost everything I can think of and it is still so slow and crashes multiple times per day.

Here are some details:

Premiere 2019, version 13.1.5

4K, 10bit, 422, 23.997fps footage (with additional archival footage and downloaded footage of varying sizes)

720 Proxies (GoPro), 4K timeline

Late 2015 iMac

4 Ghz Quad Core i7, 32GB RAM

AMD Radeon R9 4GB graphics

Working off of a 10TB harddrive with 310mp/s read/write speed

Things I have tried/do:

• Proxies
• keeping my cache empty on a regular basis
• Keeping the rest of my computer totally clean of useless stuff
• Segmenting the 70 minute sequnce into 5 chapters (nested sequences), which helped reducing crashing, but didn't help the speed
• Going to try to work it in Premiere 2020 today; I am always nervous about changing software mid-project because it's hurt me before, but it's worth a shot
• Using GPU acceleration
• Optimizing for Performance

I am really at a loss and would love further suggestions. Will ocmment on how the new 2020 does after a day of working with it.