2nd m.2 slot on asus x570 pro

[Wagz3]

Hi, I have a decent build with a 3070, 5600x on an asus prime x570 pro.  For boot drive, have an 1TB inland for os and such and has worked fine, gen pcie 3.0.  It's full, so I'm looking to add a 2nd m.2 to the 2nd m.2 slot on the board.   This will work of chipset and use some of the lanes.  As far as I know it will not affect anything with the 1st m.2 using the 16 lanes.  I have called asus to try to figure out exactly what's compatible. I guess any nvme m.2 with work, not said about sata.  This willl be for game storage.  I know the 2nd m.2 is signifigantly slower working off chipset.  I have looked at all reviews between 3.0 and 4.0 and it generally seems not worth it to gain .5 to 1 second.  All connections are gen 4 pcie.  Didn't bother worth 4.0 on main drive.  Wondering if because 2nd m.2 drive is already slowed down from being on chipset, and gen 4 pcie might actually make a difference.  Prices are getting pretty close gen 4 vs 3. like 20-30 dollars maybe at most compared to ss 970 evo plus.  Course Asus recomended using 4.0 but not sure if it will actually give faster speeds on 2nd m.2 slot which has heat sink.  going to go 2 TB.  Any recomendations would be great.  2nd m.2 info is not great in user manual or anywhere.  When i do crucial checker, they always assume i'm using main m.2 cpu slot.  Thanks.

[NewMaxx]

Any NVMe will work, some drives fare better than others on chipset (my SM2262EN drives struggle more). Performance is weaker due to higher latency but also the X570 default payload size is small which affects some drives (the SN850 had a firmware fix for this).