W500 - 4GB versus 8GB

[PeterNC]

No longer needed.

[dr_st]

If you open many documents, spreadsheets, tabs at the same time, then - yes.

[PeterNC]

No longer needed.

[pianowizard]

W500 already has SSD.

That's all the more reason to go for 8GB of RAM, so you can disable the page file and reduce the number of write cycles on the SSD. I disable the page file on my Surface and HP detachables, which both have 4GB RAM, and once in a while I get a "low memory" warning even though I don't have that many programs running.

[dr_st]

You shouldn't disable the page file altogether, but you can shrink it. Reducing the number of write cycles on an SSD is not a target worth pursuing unless you are talking about old first-gen crappy SSDs.

[axur-delmeria]

One way to check is to use the W500 normally while keeping Task Manager open and keeping a close watch on the RAM usage.

If you consistently exceed 80% RAM usage, then adding more RAM might be a good idea.
On the other hand, since you already have an SSD, the slowdown caused by using the page file/swap file/virtual memory would be nowhere as severe compared to a computer equipped with an HDD.

If you're experiencing some performance issues, keep an eye on CPU usage %, since Windows 10 is notorious for doing background tasks like downloading and installing OS updates.