OldFatGuy: ADDED:
Here is what's in my laptop (see screenshot showing my disk drives). The second one isn't bad either... it's a hybrid SSD/7200RPMHDD that's 2TB. This laptop is amazing... it has a 1080 in it too.
Nice hardware you got there :P.
Well, I "only" have a "poor man's"
850 EVO (which is SATA, not PCIe/NVMe mind you) and I'm still blown away. Like I said before, your CPU will also matter a lot with regards to booting time, especially when paired with an NVMe.
I have a friend that had upgraded to the same SSD model I have, but had an i3, and his boot times were still in the 6-7s range - of course, still an improvement over classic HDDs, but nowhere near mine.
NVMes will of course blow away even regular SSDs in high-bandwidth or massively I/O intensive applications, but again you will typically see those on a server, not a desktop/laptop. The OS boot time is one of those few exceptions where you're seeing a noticeable difference between the two.
To throw in some numbers, the SATA SSDs can benefit from a bandwidth of up to 6.0 Gbit/s, whereas PCIe/NVMes can get up to 31.5 Gbit/s, so NVMes can be, at least in terms of max theoretical peaks, 5+ times faster than regular SSDs. Expect those babies to get hot doing it, but not to worry, most come with inbuilt thermal protection so they won't fry (yes, you can read it as "throttling" :).
As for how they act, yes, you could say it's akin to persistent RAM memory (especially the ones which use some form of caching), but in essence even NVMes are still mostly based on flash memory, which is the low-cost, run of the mill electronic memory in wide use these days - the high performance I/O hardware controllers they are built around is where the real magic happens and the reason for their price range.