bobkn said:
What adapter are you looking at? I'm not that familiar with them.

I very much doubt that you'd get more than X4 performance, regardless of the number of lanes the adapter supports. Just like I get no advantage plugging my old Intel 750 AIC NVME AIC (add in card, not an M.2) into an X16 slot.

That chart in post 2 is nice, but it's inconsistent with the text in the link, and with other references. The bandwidth of a PCI-E 3.0 bus is supposed to be about 1GBps per lane (unidirectional), so a PCI-E 3.0 X4 bus (4 GBps) can keep up with the data rates that the Samsung drive that interests you is spec'd at.
It is an adapter I found on Newegg.ca and I would have had my questions answered if I had read the reviews -->I was under the mistaken impression that it was a x16 PCI-e adapter, but the seller contacted me and explained that the listing says x4, x8, and x16 only because 'fits' into those slots. It doesn't actually benefit from being in a x16 slot in any way. Only the first 32 pins of the adapter are actually wired to anything (you can see it in the photos). But the item achieves its advertised speeds and works well, so I'm leaving a 5-star review. It does what it claims to do.

The advertising for this adapter card is a bit misleading. I placed the order and I do have a spare X4 slot.

Thanks everyone for replying,
Ak