The advantage of nvme ssd vs (m2 or not) sata ssd lies in copying big files. This is an oversimplification but I think is enough for you to make a decision.
Boot time can be divided into two part: hardware/bios POST, OS boot.
BIOS POST won't be affected whether you have nvme or not. It does fluctuate if you have a lot of devices connected.
OS (hard) boot is never big files operation. It is always lots of small files loaded and executed etc. Soft boot (e.g. suspend to disk) is another story - this is just an educated guess, I might be wrong - could possibly be big image file loadout operation to ram.
So I'd say not much difference going nvme to decrease boot time against sata ssd. Even desktop programs might not see much improvement. But games which copies big resource files, media creation/editing, might see more.
Yeah, that's what I was thinking.
I'll probably just get a normal 2.5" SATA SSD. As the motherboard I am going with only has a rear M.2 slot and I have read it will overheat in this case. I am still unsure if a thermal pad would help dissipate the heat ether and don't want to take the chance it not working out.
If I need faster storage I plan on getting that SilverStone ECM23 at a later date.