With the amount of back up capacity you have, do you need that much storage? If not, then performance, no?
It would be nice to have 1 TB of storage in the laptop itself so I can carry more around. Whichever trade-off I make, though, I will be able to upgrade either capacity or performance later.
That said, I chose the 512 GB NVMe SSD for the lower latency, especially since I plan to share my home directory between OpenBSD and Fedora as an ext3 filesystem, which means I can't use soft dependencies on OpenBSD, which means that all metadata operations are synchronous.