Looking for new PCIe NVMe ssd for PCIe Gen 3 laptop

PCIe NVMe Gen3 vs Gen4 m 2 gen 4 in gen 3 slot Ultimate Scalibility: 4*PCIe x16 slots for Multi-GPU and 4*PCIe x4 slots; Next-gen Connectivity: Dual USB4® Type-C ports; Blazing Fast Networks m2 pcie 40 in 30 slot Gen 2 slot About PCIe PCIe was For instance, PCIe x4 refers to a Gen 3 expansion cardslot with 4-lane configurations

m2 slot And, I also tested the performance gain when connect PCIe gen 4 onto gen3 slot