I bought the new Samsung 980 Pro 1TB (PCIe 4.0) and put in the Lenovo Yoga Slim 7 (PCIe 3.0), I saw only ~10% decrease in raw performance : r/AMDLaptops
Sequential IO Performance - The Samsung 980 PRO PCIe 4.0 SSD Review: A Spirit of Hope
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Samsung SSD 980 Pro Review: Blazing Fast PCIe 4.0 Storage | HotHardware
980 PRO PCIe 4.0 NVMe SSD 500GB Memory & Storage - MZ-V8P500B/AM | Samsung US
Samsung 980 Pro 500GB PCIe Gen4 NVMe SSD Benchmarks Review - Page 2 of 3