The OP's first option is two different SSDs (1 TB SN850X + 1 TB something that works), and the second option is a single Fury Renegade 2 TB. Did I get that right?
Whatever you choose, there's no point in buying two smaller SSDs. A single larger unit gives you:
- one more free M.2 slot
- more flexibility in sizing the partitions, and the option to have a single 2 TB partition of course
- more flexibility in sizing the free space for overprovisioning, if you think you need some
- larger SLC cache in general (depends on the model but it certainly isn't smaller on the 2TB version)
- slightly better performance in MB/s and IOPS (which is equally unimportant as the difference between SN850x/KC3000/990Pro).
The Fury Renegade and the KC3000 are basically the same, and also the same as other SSDs with the same E18 controller inside - but others cost more.
I'd only recommend two smaller SSDs if you're planning to take one of them to a different PC or convert it to an external SSD at a later time. Also if you're going to set up a dual-boot system, because modern OSes pretty much actively hate each other, and separate SSDs serve as a means of isolation. (But before giving advice, I must admit that I screwed up my dual-SSD, dual-boot system with Windows 7 and Windows 10 nevertheless, and have yet to fix the newer of them).