Unless you're a heavy power user and counting cycles, I don't think it's going to matter to you. Going to m.2 for both of my OSes was like adding lightning to the whole system, and now that I've converted all other drives except one to SSD, storage is the least of the bottlenecks. The one thing (that you may already know) is to install Windows first, since it assumes and wants to be the only OS. Also makes the booting setup easier, although there can still be issues and compromises on the menu. Once things get settled you can do like I do and have Linux be the default boot and use F8 or whatever to get to Windows when you want.

But as far as maxxing out things, if anything I'd look to see which slot is likely to run the hottest because of airflow and location, and put the less run OS there (assuming Windows). I haven't noticed any high temps with mine (as in too high, they do run HOT), but every setup is different.

I put two identical drives in my build - that was a mistake. I can never tell which is which. :) I’m sure I’ve had each OS on each drive, and if there was a difference in performance - I’ve never noticed it.

I’d put the Linux drive first as you’ll probably migrate to using only that over time. Let windows share. But I honestly don’t think you’ll notice any difference.