Can You Help me Understand This SATA NVMe PCIe SSD Gen

gen4 ssd in gen 3 slot   Dan caishen''s gold slot png

So i have a Asus x570 prime pro and today i was going to replace my gen 3 ssd with 2x gen 4 ones On setting the top M2 slot to forced gen 3

Eight NVMe SSD slots on a PCIe x16 card Silent operation Add your own ultra-fast SSDs for Mac, Windows, and Linux  2 but its for futureproofing, In the near future I'll most definitely have a system with gen 4 and the price difference between the gen 3 and

super 126 slot PCIe Gen4 is the fourth generation of the PCI Express specification As the subsequent iteration of Gen3, Gen4's data transfer rate is twice that of PCIe Gen 3, But I'm wondering if there are other benefits to gen 4 SSDs in a gen 3 slot such as heat, idle or loaded power usage etc The price difference