Bottle neck in Win PC build

I have 64Gb ram ddr4 2400mhz with good cl times
I run Resolve and all software folders in internal NVMe 1Tb 1Gbps Pcie 3.0
I read footage (OCF) from external ssd between 500 and 800Mb/s or somethimes pro HDD at 280Mb/s (Seagate exos)
CPU is ryzen 5900x 12/24 4GHz on X570 chipset.
GPU is RTX3090 24Gb Founders Edition.
Windows 10 latest stable.

I am editing BMPCC6K @6K 24p and Ursa Cine 12K @4K 24p all DCI resolution at 3:1 compresion Braw.

Sometimes it plays fine, sometimes it stutters.

What is the weakest point in my pc build and workflow?

Your external SSD is the bottleneck, or at least it's much faster
if you use an internal M.2 where you can get 50 times the speed.

800 mbps is only 100 MB/s.
Your 4k DCI BRAW 3:1 files have a data rate of about 130 MB/s ...

With an internal PCIe-3 M.2 SSD you can easily reach real 2000 MB/s.

Your external SSD is the bottleneck, or at least it's much faster
if you use an internal M.2 where you can get 50 times the speed.

800 mbps is only 100 MB/s.
Your 4k DCI BRAW 3:1 files have a data rate of about 130 MB/s ...

With an internal PCIe-3 M.2 SSD you can easily reach real 2000 MB/s.

I guess I was wrong, I meant all speeds in Mb/s. I tested the slowest drive I mentioned with CrystalDiskMark and it's 287Mb/s