Asus Tuf Gaming Z890 pro with Ultra 9 285k - best M2 slot for OS?

So this board comes with four M2 slots. I have two 2TB cards, one runs up to 14,900MB/s in PCIe 5, the other at about 800MB/s (salvaged from an unused external usb drive). RTX5080GPU is in.

I am mostly video editing, which involves processing and moving around big files.

I am assuming my OS should go on the slower drive in one of the other three slots, and I keep the primary M2 slot for data. Is this correct, and if so, which is the best slot for the OS? I have got completely lost reading up about lane sharing and some slots being direct to the CPU and others to the z890 chipset.