2TB or 4TB drive upgrade?

[ABCbits]

If you're looking for an additional SSD, this might be a decent option. However, the first thing that stands out in its specs is a TBW of only 540, which is quite low for an SSD with this much storage capacity.

Allow me to counter this argument: for most users, this will be more than enough. If you check your current drive's SMART data, it should give you a good idea of how much "write data" you use.
If you only store a blockchain, you'll use at most a few percent of this 540 TBW if you have 8 GB RAM. With more RAM, it'll write less.

Yeah, i would rather looking at flash type, brand reputation and actual review with benchmark. Based on my past experience, SSD with QLC flash have terrible speed after it's cache fully used.

[LoyceV]

Based on my past experience, SSD with QLC flash have terrible speed after it's cache fully used.

This is something most "normal" users will probably never experience, but indeed, it's terrible for sustained writes (such as IBD). I have several HDDs that drop to literally kilobytes per second when writing a few hundred GB, and luckily I only have one SSD with this problem. It's less terrible than the HDDs, but when it happens, the entire system feels like it's "hanging".

[ABCbits]

Based on my past experience, SSD with QLC flash have terrible speed after it's cache fully used.

This is something most "normal" users will probably never experience, but indeed, it's terrible for sustained writes (such as IBD). I have several HDDs that drop to literally kilobytes per second when writing a few hundred GB, and luckily I only have one SSD with this problem. It's less terrible than the HDDs, but when it happens, the entire system feels like it's "hanging".

I somewhat disagree. With assumption typical QLC SSD have no DRAM and use pSLC as cache, "normal" user just need to copy/write files with total size a quarter of the SSD capacity. It could be less than a quarter before they notice the slow speed if the SSD also used as OS and other pSLC behavior that i don't know.